Avaccine is a biologicalpreparation that provides activeacquired immunity to a particularinfectious ormalignant disease.[1][2] The safety and effectiveness of vaccines has been widely studied and verified.[3][4] A vaccine typically contains an agent that resembles a disease-causing microorganism and is often made from weakened or killed forms of the microbe, its toxins, or one of its surface proteins. The agent stimulates the body's immune system to recognize the agent as a threat, destroy it, and recognize further and destroy any of the microorganisms associated with that agent that it may encounter in the future.
The administration of vaccines is calledvaccination. Vaccination is the most effective method of preventing infectious diseases;[10] widespread immunity due to vaccination is largely responsible for theworldwide eradication ofsmallpox and the restriction of diseases such aspolio,measles, andtetanus from much of the world. TheWorld Health Organization (WHO) reports that licensed vaccines are available for twenty-five differentpreventable infections.[11]
The first recorded use ofinoculation to prevent smallpox occurred in the 16th century in China, with the earliest hints of the practice in China coming during the 10th century.[12] It was also the first disease for which a vaccine was produced.[13][14] The folk practice ofinoculation againstsmallpox was brought from Turkey to Britain in 1721 byLady Mary Wortley Montagu.[15]The termsvaccine andvaccination are derived fromVariolae vaccinae (smallpox of the cow), the term devised byEdward Jenner (who both developed the concept of vaccines and created the first vaccine) to denotecowpox. He used the phrase in 1798 for the long title of hisInquiry into the Variolae vaccinae Known as the Cow Pox, in which he described the protective effect of cowpox against smallpox.[16] In 1881, to honor Jenner,Louis Pasteur proposed that the terms should be extended to cover the new protective inoculations then being developed.[17] The science of vaccine development and production is termedvaccinology.
Infectious diseases before and after a vaccine was introduced. Vaccinations have a direct effect on the diminishment of the number of cases and contributes indirectly to a diminishment of the number of deaths.
Effectiveness
A child withmeasles, a vaccine-preventable disease[18]
There is overwhelming scientific consensus that vaccines are a very safe and effective way to fight and eradicate infectious diseases.[19][20][21][22] Theimmune system recognizes vaccine agents as foreign, destroys them, and "remembers" them. When thevirulent version of an agent is encountered, the body recognizes the protein coat on the agent, and thus is prepared to respond, by first neutralizing the target agent before it can enter cells, and secondly by recognizing and destroying infected cells before that agent can multiply to vast numbers.[23][24]
In 1958, there were 763,094 cases of measles in the United States; 552 deaths resulted.[25][26] After the introduction of new vaccines, the number of cases dropped to fewer than 150 per year (median of 56).[26] In early 2008, there were 64 suspected cases of measles. Fifty-four of those infections were associated with importation from another country, although only thirteen percent were actually acquired outside the United States; 63 of the 64 individuals either had never been vaccinated against measles or were uncertain whether they had been vaccinated.[26]
The measles vaccine is estimated to prevent a million deaths every year.[27]
Vaccines led to the eradication ofsmallpox, one of the most contagious and deadly diseases in humans.[28] Other diseases such as rubella,polio, measles, mumps,chickenpox, andtyphoid are nowhere near as common as they were a hundred years ago thanks to widespread vaccination programs. As long as the vast majority of people are vaccinated, it is much more difficult for an outbreak of disease to occur, let alone spread. This effect is calledherd immunity. Polio, which is transmitted only among humans, is targeted by an extensiveeradication campaign that has seen endemic polio restricted to only parts of three countries (Afghanistan, Nigeria, and Pakistan).[29] However, the difficulty of reaching all children, cultural misunderstandings, anddisinformation have caused the anticipated eradication date to be missed several times.[30][31][32][33]
Vaccines also help prevent the development of antibiotic resistance. For example, by greatly reducing the incidence of pneumonia caused byStreptococcus pneumoniae, vaccine programs have greatly reduced the prevalence of infections resistant to penicillin or other first-line antibiotics.[34]
Limitations
Limitations to their effectiveness, nevertheless, exist.[35] Sometimes, protection fails for vaccine-related reasons such as failures in vaccine attenuation, vaccination regimens or administration.[36]
Failure may also occur for host-related reasons if the host's immune system does not respond adequately or at all. Host-related lack of response occurs in an estimated 2-10% of individuals, due to factors including genetics, immune status, age, health and nutritional status.[36] One type ofprimary immunodeficiency disorder resulting in genetic failure isX-linked agammaglobulinemia, in which the absence of an enzyme essential forB cell development prevents the host's immune system from generatingantibodies to apathogen.[37][38]
Host–pathogen interactions and responses to infection are dynamic processes involving multiple pathways in the immune system.[39][40] A host does not develop antibodies instantaneously: while the body'sinnate immunity may be activated in as little as twelve hours,adaptive immunity can take 1–2 weeks to fully develop. During that time, the host can still become infected.[41]
Once antibodies are produced, they may promote immunity in any of several ways, depending on the class of antibodies involved. Their success in clearing or inactivating a pathogen will depend on the amount of antibodies produced and on the extent to which those antibodies are effective at countering the strain of the pathogen involved, since different strains may be differently susceptible to a given immune reaction.[40] In some cases vaccines may result in partial immune protection (in which immunity is less than 100% effective but still reduces risk of infection) or in temporary immune protection (in which immunity wanes over time) rather than full or permanent immunity. They can still raise the reinfection threshold for the population as a whole and make a substantial impact.[42] They can also mitigate the severity of infection, resulting in a lowermortality rate, lowermorbidity, faster recovery from illness, and a wide range of other effects.[43][44]
Those who are older often display less of a response than those who are younger, a pattern known asImmunosenescence.[45]Adjuvants commonly are used to boost immune response, particularly for older people whose immune response to a simple vaccine may have weakened.[46]
Theefficacy or performance of the vaccine is dependent on several factors:
the disease itself (for some diseases vaccination performs better than for others)
the strain of vaccine (some vaccines are specific to, or at least most effective against, particular strains of the disease)[47]
idiosyncratic response to vaccination; some individuals are "non-responders" to certain vaccines, meaning that they do not generate antibodies even after being vaccinated correctly.
assorted factors such as ethnicity, age, or genetic predisposition.
If a vaccinated individual does develop the disease vaccinated against (breakthrough infection), the disease is likely to be less severe and less transmissible than in unvaccinated cases.[48][49]
Important considerations in an effective vaccination program:[50]
careful modeling to anticipate the effect that an immunization campaign will have on the epidemiology of the disease in the medium to long term
ongoing surveillance for the relevant disease following introduction of a new vaccine
maintenance of high immunization rates, even when a disease has become rare
Vaccinations given to children, adolescents, or adults are generally safe.[51][52] Adverse effects, if any, are generally mild.[53] The rate of side effects depends on the vaccine in question.[53] Some common side effects include fever, pain around the injection site, and muscle aches.[53] Additionally, some individuals may be allergic to ingredients in the vaccine.[54] TheMMR vaccine is rarely associated withfebrile seizures.[52]
At least 19 countries have no-fault compensation programs to provide compensation for those with severe adverse effects of vaccination.[55] The United States' program is known as theNational Childhood Vaccine Injury Act, and the United Kingdom employs theVaccine Damage Payment.
Types
Vaccines typically contain attenuated, inactivated or dead organisms or purified products derived from them. There are several types of vaccines in use.[56] These represent different strategies used to try to reduce the risk of illness while retaining the ability to induce a beneficial immune response.
Some vaccines contain live,attenuated microorganisms. Many of these are activeviruses that have been cultivated under conditions that disable their virulent properties, or that use closely related but less dangerous organisms to produce a broad immune response. Although most attenuated vaccines are viral, some are bacterial in nature. Examples include the viral diseasesyellow fever,measles,mumps, andrubella, and the bacterial diseasetyphoid. The liveMycobacteriumtuberculosis vaccine developed by Calmette and Guérin is not made of acontagious strain but contains a virulently modified strain called "BCG" used to elicit an immune response to the vaccine. The live attenuated vaccine containing strainYersinia pestis EV is used forplague immunization. Attenuated vaccines have some advantages and disadvantages. Attenuated, or live, weakened, vaccines typically provoke more durable immunological responses. Attenuated vaccines also elicit a cellular and humoral response. However, they may not be safe for use in immunocompromised individuals, and on rare occasions mutate to a virulent form and cause disease.[57]
Toxoid vaccines are made from inactivated toxic compounds that cause illness rather than the microorganism.[59] Examples of toxoid-based vaccines includetetanus anddiphtheria.[59] Not all toxoids are for microorganisms; for example,Crotalus atrox toxoid is used to vaccinate dogs againstrattlesnake bites.[60]
Rather than introducing an inactivated or attenuated microorganism to an immune system (which would constitute a "whole-agent" vaccine), asubunit vaccine uses a fragment of it to create an immune response. One example is the subunit vaccine againsthepatitisB, which is composed of only the surface proteins of the virus (previously extracted from theblood serum of chronically infected patients but now produced byrecombination of the viral genes intoyeast).[61] Other examples include theGardasilvirus-like particlehuman papillomavirus (HPV) vaccine,[62] thehemagglutinin andneuraminidase subunits of theinfluenza virus,[59] andedible algae vaccines. A subunit vaccine is being used for plague immunization.[63]
Heterologous vaccines also known as "Jennerian vaccines", are vaccines that are pathogens of other animals that either do not cause disease or cause mild disease in the organism being treated. The classic example is Jenner's use of cowpox to protect against smallpox. A current example is the use ofBCG vaccine made fromMycobacterium bovis to protect againsttuberculosis.[67]
Genetic vaccines are based on the principle of uptake of a nucleic acid into cells, whereupon a protein is produced according to the nucleic acid template. This protein is usually the immunodominant antigen of the pathogen or a surface protein that enables the formation of neutralizing antibodies. The subgroup of genetic vaccines encompass viral vector vaccines, RNA vaccines and DNA vaccines.[citation needed]
Viral vector vaccines use a safevirus to insert pathogen genes in the body to produce specificantigens, such as surfaceproteins, to stimulate animmune response.[68][69] Viruses being researched for use as viral vectors include adenovirus, vaccinia virus, andVSV.
A DNA vaccine uses aDNAplasmid (pDNA)) that encodes for an antigenic protein originating from the pathogen upon which the vaccine will be targeted. pDNA is inexpensive, stable, and relatively safe, making it an excellent option for vaccine delivery.[74]
This approach offers a number of potential advantages over traditional approaches, including the stimulation of both B- and T-cell responses, improved vaccine stability, the absence of any infectious agent and the relative ease of large-scale manufacture.[75]
Experimental
Many innovative vaccines are also in development and use.
Dendritic cell vaccines combinedendritic cells with antigens to present the antigens to the body's white blood cells, thus stimulating an immune reaction. These vaccines have shown some positive preliminary results for treating brain tumors[76] and are also tested in malignant melanoma.[77]
Recombinantvector – by combining the physiology of one microorganism and theDNA of another, immunity can be created against diseases that have complex infection processes. An example is theRVSV-ZEBOV vaccine licensed to Merck that is being used in 2018 to combatebola in Congo.[78]
Targeting of identified bacterial proteins that are involved in complement inhibition would neutralize the key bacterial virulence mechanism.[79]
The use ofplasmids has been validated in preclinical studies as a protective vaccine strategy for cancer and infectious diseases. However, in human studies, this approach has failed to provide clinically relevant benefit. The overall efficacy of plasmid DNA immunization depends on increasing the plasmid'simmunogenicity while also correcting for factors involved in the specific activation of immune effector cells.[80]
Inverse vaccines are vaccines that train the immune system to not respond to certain substances.
While most vaccines are created using inactivated or attenuated compounds from microorganisms,synthetic vaccines are composed mainly or wholly of synthetic peptides, carbohydrates, or antigens.[citation needed]
Valence
Vaccines may bemonovalent (also calledunivalent) ormultivalent (also calledpolyvalent). A monovalent vaccine is designed to immunize against a single antigen or single microorganism.[83] A multivalent or polyvalent vaccine is designed to immunize against two or more strains of the same microorganism, or against two or more microorganisms.[84] The valency of a multivalent vaccine may be denoted with a Greek or Latin prefix (e.g.,bivalent,trivalent, ortetravalent/quadrivalent). In certain cases, a monovalent vaccine may be preferable for rapidly developing a strong immune response.[85]
Interactions
When two or more vaccines are mixed in the same formulation, the two vaccines can interfere. This most frequently occurs with live attenuated vaccines, where one of the vaccine components is more robust than the others and suppresses the growth and immune response to the other components.[86]
This phenomenon was noted in the trivalent Sabinpolio vaccine, where the relative amount of serotype2 virus in the vaccine had to be reduced to stop it from interfering with the "take" of the serotype1 and3 viruses in the vaccine. To accomplish this, the doses of serotypes1 and3 were increased in the vaccine in the early 1960s.[87] It was also noted in a 2001 study to be a problem withdengue vaccines, where the DEN-3 serotype was found to predominate and suppress the response to DEN-1, -2 and -4 serotypes.[88]
Graphic from the World Health Organization describing the main ingredients typically in vaccinesA vaccine dose contains many ingredients (such as stabilizers, adjuvants, residual inactivating ingredients, residual cell culture materials, residual antibiotics and preservatives) very little of which is the active ingredient, theimmunogen. A single dose may have merely nanograms of virus particles, or micrograms of bacterial polysaccharides. A vaccine injection, oral drops or nasal spray is mostly water. Other ingredients are added to boost the immune response, to ensure safety or help with storage, and a tiny amount of material is left-over from the manufacturing process. Very rarely, these materials can cause an allergic reaction in people who are very sensitive to them.
Vaccines typically contain one or moreadjuvants, used to boost the immune response. Tetanus toxoid, for instance, is usually adsorbed ontoalum. This presents the antigen in such a way as to produce a greater action than the simple aqueous tetanus toxoid. People who have an adverse reaction to adsorbed tetanus toxoid may be given the simple vaccine when the time comes for a booster.[89]
In the preparation for the 1990 Persian Gulf campaign, the whole cellpertussis vaccine was used as an adjuvant foranthrax vaccine. This produces a more rapid immune response than giving only the anthrax vaccine, which is of some benefit if exposure might be imminent.[90]
Many vaccines need preservatives to prevent serious adverse effects such asStaphylococcus infection, which in one 1928 incident killed 12 of 21 children inoculated with adiphtheria vaccine that lacked a preservative.[94] Several preservatives are available, including thiomersal,phenoxyethanol, andformaldehyde. Thiomersal is more effective against bacteria, has a better shelf-life, and improves vaccine stability, potency, and safety; however, in the U.S., theEuropean Union, and a few other affluent countries, it is no longer used as a preservative in childhood vaccines, as a precautionary measure due to itsmercury content.[95] Althoughcontroversial claims have been made that thiomersal contributes toautism, no convincing scientific evidence supports these claims.[96] Furthermore, a 10–11-year study of 657,461 children found that theMMR vaccine does not cause autism and actually reduced the risk of autism by seven percent.[97][98]
Excipients
Beside the active vaccine itself, the followingexcipients and residual manufacturing compounds are present or may be present in vaccine preparations:[99]
Aluminum salts or gels are added asadjuvants. Adjuvants are added to promote an earlier, more potent response, and more persistent immune response to the vaccine; they allow for a lower vaccine dosage.
Antibiotics are added to some vaccines to prevent the growth of bacteria during production and storage of the vaccine.
Formaldehyde is used to inactivate bacterial products for toxoid vaccines. Formaldehyde is also used to inactivate unwanted viruses and kill bacteria that might contaminate the vaccine during production.
Monosodium glutamate (MSG) and 2-phenoxyethanol are used as stabilizers in a few vaccines to help the vaccine remain unchanged when the vaccine is exposed to heat, light, acidity, or humidity.
Thiomersal is a mercury-containing antimicrobial that is added to vials of vaccines that contain more than one dose to prevent contamination and growth of potentially harmful bacteria. Due to the controversy surrounding thiomersal, it has been removed from most vaccines except multi-use influenza, where it was reduced to levels so that a single dose contained less than a microgram of mercury, a level similar to eating ten grams of canned tuna.[100]
Nomenclature
Various fairly standardized abbreviations for vaccine names have developed, although the standardization is by no means centralized or global. For example, the vaccine names used in the United States have well-established abbreviations that are also widely known and used elsewhere. An extensive list of them provided in a sortable table and freely accessible is available at a USCenters for Disease Control and Prevention web page.[101] The page explains that "The abbreviations [in] this table (Column 3) were standardized jointly by staff of the Centers for Disease Control and Prevention,ACIP Work Groups, the editor of theMorbidity and Mortality Weekly Report (MMWR), the editor ofEpidemiology and Prevention of Vaccine-Preventable Diseases (the Pink Book), ACIP members, and liaison organizations to the ACIP."[101]
Some examples are "DTaP" for diphtheria and tetanus toxoids and acellular pertussis vaccine, "DT" for diphtheria and tetanus toxoids, and "Td" for tetanus and diphtheria toxoids. At its page on tetanus vaccination,[102] the CDC further explains that "Upper-case letters in these abbreviations denote full-strength doses of diphtheria (D) and tetanus (T) toxoids and pertussis (P) vaccine. Lower-case "d" and "p" denote reduced doses of diphtheria and pertussis used in the adolescent/adult-formulations. The 'a' in DTaP and Tdap stands for 'acellular', meaning that the pertussis component contains only a part of the pertussis organism."[102]
Another list of established vaccine abbreviations is at the CDC's page called "Vaccine Acronyms and Abbreviations", with abbreviations used on U.S. immunization records.[103] TheUnited States Adopted Name system has some conventions for theword order of vaccine names, placinghead nouns first andadjectives postpositively. This is why the USAN for "OPV" is "poliovirus vaccine live oral" rather than "oral poliovirus vaccine".
A vaccinelicensure occurs after the successful conclusion of the development cycle and further the clinical trials and other programs involved throughPhasesI–III demonstrating safety, immunoactivity, immunogenetic safety at a given specific dose, proven effectiveness in preventing infection for target populations, and enduring preventive effect (time endurance or need for revaccination must be estimated).[104] Because preventive vaccines are predominantly evaluated in healthy population cohorts and distributed among the general population, a high standard of safety is required.[105] As part of a multinational licensing of a vaccine, the World Health OrganizationExpert Committee on Biological Standardization developed guidelines of international standards for manufacturing andquality control of vaccines, a process intended as a platform for national regulatory agencies to apply for their own licensing process.[104] Vaccine manufacturers do not receive licensing until a complete clinical cycle of development and trials proves the vaccine is safe and has long-term effectiveness, following scientific review by a multinational or national regulatory organization, such as theEuropean Medicines Agency (EMA) or the USFood and Drug Administration (FDA).[106][107]
Upondeveloping countries adopting WHO guidelines for vaccine development and licensure, each country has its own responsibility to issue a national licensure, and to manage, deploy, and monitor the vaccine throughout its use in each nation.[104] Building trust and acceptance of a licensed vaccine among the public is a task of communication by governments and healthcare personnel to ensure a vaccination campaign proceeds smoothly, saves lives, and enables economic recovery.[108][109] When a vaccine is licensed, it will initially be in limited supply due to variable manufacturing, distribution, and logistical factors, requiring an allocation plan for the limited supply and which population segments should be prioritized to first receive the vaccine.[108]
The process requires manufacturing consistency at WHO-contracted laboratories followingGood Manufacturing Practice (GMP).[104] When UN agencies are involved in vaccine licensure, individual nations collaborate by 1) issuing marketing authorization and a national license for the vaccine, its manufacturers, and distribution partners; and 2) conductingpostmarketing surveillance, including records for adverse events after the vaccination program. The WHO works with national agencies to monitor inspections of manufacturing facilities and distributors for compliance with GMP and regulatory oversight.[104]
Some countries choose to buy vaccines licensed by reputable national organizations, such as EMA, FDA, or national agencies in other affluent countries, but such purchases typically are more expensive and may not have distribution resources suitable to local conditions in developing countries.[104]
European Union
In the European Union (EU), vaccines for pandemic pathogens, such asseasonal influenza, are licensed EU-wide where all themember states comply ("centralized"), are licensed for only some member states ("decentralized"), or are licensed on an individual national level.[106] Generally, all EU states follow regulatory guidance and clinical programs defined by the EuropeanCommittee for Medicinal Products for Human Use (CHMP), a scientific panel of theEuropean Medicines Agency (EMA) responsible for vaccine licensure.[106] The CHMP is supported by several expert groups who assess and monitor the progress of a vaccine before and after licensure and distribution.[106]
United States
Under the FDA, the process of establishing evidence for vaccine clinical safety and efficacy is the same as forthe approval process for prescription drugs.[110] If successful through the stages of clinical development, the vaccine licensing process is followed by aBiologics License Application which must provide a scientific review team (from diverse disciplines, such as physicians, statisticians, microbiologists, chemists) and comprehensive documentation for the vaccine candidate having efficacy and safety throughout its development. Also during this stage, the proposed manufacturing facility is examined by expert reviewers for GMP compliance, and the label must have a compliant description to enable health care providers' definition of vaccine-specific use, including its possible risks, to communicate and deliver the vaccine to the public.[110] After licensure, monitoring of the vaccine and its production, including periodic inspections for GMP compliance, continue as long as the manufacturer retains its license, which may include additional submissions to the FDA of tests for potency, safety, and purity for each vaccine manufacturing step.[110]
India
In India, theDrugs Controller General, the head of department of theCentral Drugs Standard Control Organization, India's national regulatory body for cosmetics, pharmaceuticals and medical devices, is responsible for the approval of licences for specified categories of drugs such as vaccines and other medicinal items, such as blood or blood products, IV fluids, and sera.[111]
Postmarketing surveillance
Until a vaccine is in use amongst the general population, all potentialadverse events from the vaccine may not be known, requiring manufacturers to conductPhaseIV studies forpostmarketing surveillance of the vaccine while it is used widely in the public.[104][110] The WHO works with UN member states to implement post-licensing surveillance.[104] The FDA relies on aVaccine Adverse Event Reporting System to monitor safety concerns about a vaccine throughout its use in the American public.[110]
For country-specific information on vaccination policies and practices, seeVaccination policy.
In order to provide the best protection, children are recommended to receive vaccinations as soon as their immune systems are sufficiently developed to respond to particular vaccines, with additional "booster" shots often required to achieve "full immunity". This has led to the development of complex vaccination schedules. Global recommendations of vaccination schedule are issued byStrategic Advisory Group of Experts and will be further translated byadvisory committee at the country level with considering of local factors such as disease epidemiology, acceptability of vaccination, equity in local populations, and programmatic and financial constraint.[112] In the United States, theAdvisory Committee on Immunization Practices, which recommends schedule additions for theCenters for Disease Control and Prevention, recommends routine vaccination of children against[113]hepatitis A,hepatitis B, polio, mumps, measles, rubella,diphtheria,pertussis,tetanus,HiB, chickenpox,rotavirus,influenza,meningococcal disease andpneumonia.[114]
The large number of vaccines and boosters recommended (up to 24 injections by age two) has led to problems with achieving full compliance. To combat declining compliance rates, various notification systems have been instituted and many combination injections are now marketed (e.g.,Pentavalent vaccine andMMRV vaccine), which protect against multiple diseases.
Besides recommendations for infant vaccinations and boosters, many specific vaccines are recommended for other ages or for repeated injections throughout life – most commonly for measles, tetanus, influenza, and pneumonia. Pregnant women are often screened for continued resistance to rubella. Thehuman papillomavirus vaccine is recommended in the U.S. (as of 2011)[115] and UK (as of 2009).[116] Vaccine recommendations for the elderly concentrate on pneumonia and influenza, which are more deadly to that group. In 2006, a vaccine was introduced againstshingles, a disease caused by the chickenpox virus, which usually affects the elderly.[117]
Scheduling and dosing of a vaccination may be tailored to the level of immunocompetence of an individual[118] and to optimize population-wide deployment of a vaccine when its supply is limited,[119] e.g. in the setting of a pandemic.
One challenge in vaccine development is economic: Many of the diseases most demanding a vaccine, includingHIV,malaria and tuberculosis, exist principally in poor countries. Pharmaceutical firms andbiotechnology companies have little incentive to develop vaccines for these diseases because there is little revenue potential. Even in more affluent countries, financial returns are usually minimal and the financial and other risks are great.[120]
Most vaccine development to date has relied on "push" funding by government, universities and non-profit organizations.[121] Many vaccines have been highly cost effective and beneficial forpublic health.[122] The number of vaccines actually administered has risen dramatically in recent decades.[123] This increase, particularly in the number of different vaccines administered to children before entry into schools, may be due to government mandates and support, rather than economic incentive.[124]
Patents
According to theWorld Health Organization (WHO), the biggest barrier to vaccine production in less developed countries has not beenpatents, but the substantial financial,infrastructure, and workforce requirements needed for market entry. Vaccines are complex mixtures of biological compounds, and unlike the case forprescription drugs, there are no truegeneric vaccines. The vaccine produced by a new facility must undergo complete clinical testing for safety and efficacy by the manufacturer. For most vaccines, specific processes in technology are patented. These can be circumvented by alternative manufacturing methods, but this required R&D infrastructure and a suitably skilled workforce. In the case of a few relatively new vaccines, such as thehuman papillomavirus vaccine, the patents may impose an additional barrier.[125]
When increased production of vaccines was urgently needed during theCOVID-19 pandemic in 2021, theWorld Trade Organization and governments around the world evaluated whether to waiveintellectual property rights and patents onCOVID-19 vaccines, which would "eliminate all potential barriers to the timely access of affordable COVID-19 medical products, including vaccines and medicines, and scale up the manufacturing and supply of essential medical products".[126]
Production
Vaccine production is fundamentally different from other kinds of manufacturing – including regularpharmaceutical manufacturing – in that vaccines are intended to be administered to millions of people of whom the vast majority are perfectly healthy.[127] This fact drives an extraordinarily rigorous production process with strict compliance requirements that go far beyond what is required of other products.[127]
Depending upon the antigen, it can cost anywhere from US$50 to $500 million to build a vaccine production facility, which requires highly specialized equipment,clean rooms, and containment rooms.[128] There is a global scarcity of personnel with the right combination of skills, expertise, knowledge, competence and personality to staff vaccine production lines.[128] With the notable exceptions of Brazil, China, and India, many developing countries' educational systems are unable to provide enough qualified candidates, and vaccine makers based in such countries must hire expatriate personnel to keep production going.[128]
Vaccine production has several stages. First, the antigen itself is generated. Viruses are grown either on primary cells such aschicken eggs (e.g., for influenza) or on continuous cell lines such as cultured human cells (e.g., forhepatitis A).[129] Bacteria are grown inbioreactors (e.g.,Haemophilus influenzae type b). Likewise, a recombinant protein derived from the viruses or bacteria can be generated in yeast, bacteria, or cell cultures.[130][131]
After the antigen is generated, it is isolated from the cells used to generate it. A virus may need to be inactivated, possibly with no further purification required. Recombinant proteins need many operations involving ultrafiltration and column chromatography. Finally, the vaccine is formulated by adding adjuvant, stabilizers, and preservatives as needed. The adjuvant enhances the immune response to the antigen, stabilizers increase the storage life, and preservatives allow the use of multidose vials.[130][131] Combination vaccines are harder to develop and produce, because of potential incompatibilities and interactions among the antigens and other ingredients involved.[132]
The final stage in vaccine manufacture before distribution isfill and finish, which is the process of filling vials with vaccines and packaging them for distribution. Although this is a conceptually simple part of the vaccine manufacture process, it is often a bottleneck in the process of distributing and administering vaccines.[133][134][135]
Vaccine production techniques are evolving. Culturedmammalian cells are expected to become increasingly important, compared to conventional options such as chicken eggs, due to greater productivity and low incidence of problems with contamination. Recombination technology that produces genetically detoxified vaccines is expected to grow in popularity for the production of bacterial vaccines that use toxoids. Combination vaccines are expected to reduce the quantities of antigens they contain, and thereby decrease undesirable interactions, by usingpathogen-associated molecular patterns.[132]
Vaccine manufacturers
The companies with the highest market share in vaccine production areMerck,Sanofi,GlaxoSmithKline,Pfizer andNovartis, with 70% of vaccine sales concentrated in the EU or US (2013).[136]: 42 Vaccine manufacturing plants require large capital investments ($50 million up to $300 million) and may take between 4 and 6 years to construct, with the full process of vaccine development taking between 10 and 15 years.[136]: 43 Manufacturing in developing countries is playing an increasing role in supplying these countries, specifically with regards to older vaccines and in Brazil, India and China.[136]: 47 The manufacturers in India are the most advanced in the developing world and include theSerum Institute of India, one of the largest producers of vaccines by number of doses and an innovator in processes, recently improving efficiency of producing the measles vaccine by 10 to 20-fold, due to switching to aMRC-5 cell culture instead of chicken eggs.[136]: 48 China's manufacturing capabilities are focused on supplying their own domestic need, withSinopharm (CNPGC) alone providing over 85% of the doses for 14 different vaccines in China.[136]: 48 Brazil is approaching the point of supplying its own domestic needs using technology transferred from the developed world.[136]: 49
Delivery systems
A woman receiving a vaccine by injection
One of the most common methods of delivering vaccines into the human body isinjection.
The development of new delivery systems raises the hope of vaccines that are safer and more efficient to deliver and administer. Lines of research includeliposomes andISCOM (immune stimulating complex).[137]
Notable developments in vaccine delivery technologies have included oral vaccines. Early attempts to apply oral vaccines showed varying degrees of promise, beginning early in the 20th century, at a time when the very possibility of an effective oral antibacterial vaccine was controversial.[138] By the 1930s there was increasing interest in the prophylactic value of an oraltyphoid fever vaccine for example.[139]
Anoral polio vaccine turned out to be effective when vaccinations were administered by volunteer staff without formal training; the results also demonstrated increased ease and efficiency of administering the vaccines. Effective oral vaccines have many advantages; for example, there is no risk of blood contamination. Vaccines intended for oral administration need not be liquid, and as solids, they commonly are more stable and less prone to damage or spoilage by freezing in transport and storage.[140] Such stability reduces the need for a "cold chain": the resources required to keep vaccines within a restricted temperature range from the manufacturing stage to the point of administration, which, in turn, may decrease costs of vaccines.
A microneedle approach, which is still in stages of development, uses "pointed projections fabricated into arrays that can create vaccine delivery pathways through the skin".[141]
An experimental needle-free[142] vaccine delivery system is undergoing animal testing.[143][144] A stamp-size patch similar to anadhesive bandage contains about 20,000 microscopic projections per square cm.[145] Thisdermal administration potentially increases the effectiveness of vaccination, while requiring less vaccine than injection.[146]
Vaccinations of animals are used both to prevent their contracting diseases and to prevent transmission of disease to humans.[147] Both animals kept as pets and animals raised as livestock are routinely vaccinated. In some instances, wild populations may be vaccinated. This is sometimes accomplished with vaccine-laced food spread in a disease-prone area and has been used to attempt to controlrabies inraccoons.
Cases of veterinary vaccines used in humans have been documented, whether intentional or accidental, with some cases of resultant illness, most notably withbrucellosis.[148] However, the reporting of such cases is rare and very little has been studied about the safety and results of such practices. With the advent of aerosol vaccination in veterinary clinics, human exposure to pathogens not naturally carried in humans, such asBordetella bronchiseptica, has likely increased in recent years.[148] In some cases, most notablyrabies, the parallel veterinary vaccine against a pathogen may be as much asorders of magnitude more economical than the human one.
DIVA vaccines
DIVA (Differentiation of Infected from Vaccinated Animals), also known as SIVA (Segregation of Infected from Vaccinated Animals) vaccines, make it possible to differentiate between infected and vaccinated animals. DIVA vaccines carry at least oneepitope less than the equivalent wild microorganism. An accompanying diagnostic test that detects the antibody against that epitope assists in identifying whether the animal has been vaccinated or not.[citation needed]
The first DIVA vaccines (formerly termedmarker vaccines and since 1999 coined as DIVA vaccines) and companion diagnostic tests were developed by J. T. van Oirschot and colleagues at the Central Veterinary Institute in Lelystad, The Netherlands.[149][150] They found that some existing vaccines againstpseudorabies (also termed Aujeszky's disease) had deletions in their viral genome (among which was the gE gene). Monoclonal antibodies were produced against that deletion and selected to develop anELISA that demonstrated antibodies against gE. In addition, novel genetically engineered gE-negative vaccines were constructed.[151] Along the same lines, DIVA vaccines and companion diagnostic tests against bovine herpesvirus1 infections have been developed.[150][152]
The DIVA strategy has been applied in various countries to successfully eradicate pseudorabies virus from those countries. Swine populations were intensively vaccinated and monitored by the companion diagnostic test and, subsequently, the infected pigs were removed from the population. Bovine herpesvirus1 DIVA vaccines are also widely used in practice.[citation needed] Considerable efforts are ongoing to apply the DIVA principle to a wide range of infectious diseases, such as classical swine fever,[153] avian influenza,[154]Actinobacillus pleuropneumonia[155] andSalmonella infections in pigs.[156]
Comparison ofsmallpox (left) andcowpox inoculations sixteen days after administration (1802)
Prior to the introduction of vaccination with material from cases of cowpox (heterotypic immunisation), smallpox could be prevented by deliberatevariolation with smallpox virus. According to historianJoseph Needham,Taoists in China as far back as the 10th century practiced a form of inoculation and passed it down through oral tradition, though Needham's claim has been criticized since the practice was not written about.[157][158] The Chinese also practiced the oldest documented use of variolation, dating back to the fifteenth century. They implemented a method of "nasalinsufflation" administered by blowing powdered smallpox material, usually scabs, up the nostrils. Various insufflation techniques have been recorded throughout the sixteenth and seventeenth centuries within China.[159]: 60 Two reports on the Chinese practice ofinoculation were received by theRoyal Society in London in 1700; one byMartin Lister who received a report by an employee of theEast India Company stationed in China and another byClopton Havers.[160] In France,Voltaire reports that the Chinese have practiced variolation "these hundred years".[161]
Mary Wortley Montagu, who had witnessed variolation in Turkey, had her four-year-old daughter variolated in the presence ofphysicians of the Royal Court in 1721 upon her return to England.[159] Later on that year,Charles Maitland conducted an experimental variolation of six prisoners inNewgate Prison in London.[162] The experiment was a success, and soon variolation was drawing attention from the royal family, who helped promote the procedure. However, in 1783, several days afterPrince Octavius of Great Britain was inoculated, he died.[163]
In 1796, the physicianEdward Jenner took pus from the hand of a milkmaid withcowpox, scratched it into the arm of an 8-year-old boy,James Phipps, and six weeks later variolated the boy with smallpox, afterwards observing that he did not catch smallpox.[164][165] Jenner extended his studies and, in 1798, reported that his vaccine was safe in children and adults, and could be transferred from arm-to-arm, which reduced reliance on uncertain supplies from infected cows.[163] In 1804, the SpanishBalmis smallpox vaccination expedition to Spain's colonies Mexico and Philippines used the arm-to-arm transport method to get around the fact the vaccine survived for only 12 daysin vitro. They used cowpox.[166] Since vaccination with cowpox was much safer than smallpox inoculation,[167] the latter, though still widely practiced in England, was banned in 1840.[168]
French print in 1896 marking the centenary of Jenner's vaccine
Following on from Jenner's work, the second generation of vaccines was introduced in the 1880s byLouis Pasteur who developed vaccines forchicken cholera andanthrax,[17] and from the late nineteenth century vaccines were considered a matter of national prestige. Nationalvaccination policies were adopted and compulsory vaccination laws were passed.[164] In 1931Alice Miles Woodruff andErnest Goodpasture documented that thefowlpox virus could be grown inembryonated chickenegg. Soon scientists began cultivating other viruses in eggs. Eggs were used for virus propagation in the development of ayellow fever vaccine in 1935 and aninfluenza vaccine in 1945. In 1959growth media andcell culture replaced eggs as the standard method of virus propagation for vaccines.[169]
Vaccinology flourished in the twentieth century, which saw the introduction of several successful vaccines, including those againstdiphtheria,measles,mumps, andrubella. Major achievements included the development of thepolio vaccine in the 1950s and theeradication of smallpox during the 1960s and 1970s.Maurice Hilleman was the most prolific of the developers of the vaccines in the twentieth century. As vaccines became more common, many people began taking them for granted. However, vaccines remain elusive for many important diseases, includingherpes simplex,malaria,gonorrhea, andHIV.[164][170]
Generations of vaccines
Vials of smallpox and anthrax serum
First generation vaccines are whole-organism vaccines – either live andweakened, or killed forms.[171] Live, attenuated vaccines, such as smallpox and polio vaccines, are able to inducekiller T-cell (TC or CTL) responses,helper T-cell (TH) responses and antibodyimmunity. However, attenuated forms of apathogen can convert to a dangerous form and may cause disease inimmunocompromised vaccine recipients (such as those withAIDS). While killed vaccines do not have this risk, they cannot generate specific killer T-cell responses and may not work at all for some diseases.[171]
Second generation vaccines were developed to reduce the risks from live vaccines. These are subunit vaccines, consisting of specificprotein antigens (such astetanus ordiphtheriatoxoid) orrecombinant protein components (such as the hepatitis B surfaceantigen). They can generate TH andantibody responses, but not killer T cell responses.[citation needed]
RNA vaccines andDNA vaccines are examples of third generation vaccines.[171][172][173] In 2016 a DNA vaccine for theZika virus began testing at theNational Institutes of Health. Separately, Inovio Pharmaceuticals and GeneOne Life Science began tests of a different DNA vaccine against Zika in Miami. Manufacturing the vaccines in volume was unsolved as of 2016.[174] Clinical trials for DNA vaccines to prevent HIV are underway.[175]mRNA vaccines such asBNT162b2 were developed in the year 2020 with the help ofOperation Warp Speed and massively deployed to combat theCOVID-19 pandemic. In 2021,Katalin Karikó andDrew Weissman received Columbia University's Horwitz Prize for their pioneering research in mRNA vaccine technology.[176]
Trends
This section needs to beupdated. Please help update this article to reflect recent events or newly available information.(June 2018)
Since at least 2013, scientists have been trying to develop synthetic third-generation vaccines by reconstructing the outside structure of avirus; it was hoped that this will help preventvaccine resistance.[177]
Principles that govern the immune response can now be used in tailor-made vaccines against many noninfectious human diseases, such as cancers and autoimmune disorders.[178] For example, the experimental vaccineCYT006-AngQb has been investigated as a possible treatment forhigh blood pressure.[179] Factors that affect the trends of vaccine development include progress in translatory medicine,demographics,regulatory science, political, cultural, and social responses.[180]
Plants as bioreactors for vaccine production
The idea of vaccine production viatransgenic plants was identified as early as 2003. Plants such astobacco,potato,tomato, andbanana can have genes inserted that cause them to produce vaccines usable for humans.[181] In 2005, bananas were developed that produce a human vaccine againsthepatitis B.[182]
Vaccine hesitancy
After the December 2020 introduction of COVID vaccines in the United States, a partisan gap in death rates developed, indicating the effects of vaccine skepticism.[183] As of March 2024, more than 30 percent of Republicans had not received a COVID-19 vaccine, compared with less than 10 percent of Democrats.[183]
^"Immunization: The Basics".Centers for Disease Control and Prevention. 22 November 2022.Archived from the original on 12 July 2023. Retrieved8 July 2023.
^Amanna, Ian J.; Slifka, Mark K. (2018). "Successful Vaccines". In Lars Hangartner; Dennis R. Burton (eds.).Vaccination Strategies Against Highly Variable Pathogens. Current Topics in Microbiology and Immunology, vol. 428. Vol. 428. Springer. pp. 1–30.doi:10.1007/82_2018_102.ISBN978-3-030-58003-2.PMC6777997.PMID30046984.The effect of vaccines on public health is truly remarkable. One study examining the impact of childhood vaccination on the 2001 US birth cohort found that vaccines prevented 33,000 deaths and 14 million cases of disease (Zhou et al. 2005). Among 73 nations supported by the GAVI alliance, mathematical models project that vaccines will prevent 23.3 million deaths from 2011–2020 compared to what would have occurred if there were no vaccines available (Lee et al. 2013). Vaccines have been developed against a wide assortment of human pathogens.
^*United States Centers for Disease Control and Prevention (2011).A CDC framework for preventing infectious diseases.Archived 29 August 2017 at theWayback Machine Accessed 11 September 2012. "Vaccines are our most effective and cost-saving tools for disease prevention, preventing untold suffering and saving tens of thousands of lives and billions of dollars in healthcare costs each year."
Public Health Agency of Canada.Vaccine-preventable diseases.Archived 13 March 2015 at theWayback Machine Accessed 11 September 2012. "Vaccines still provide the most effective, longest-lasting method of preventing infectious diseases in all age groups."
^Grammatikos AP, Mantadakis E, Falagas ME (June 2009). "Meta-analyses on pediatric infections and vaccines".Infectious Disease Clinics of North America.23 (2):431–457.doi:10.1016/j.idc.2009.01.008.PMID19393917.
^Reda, Shereen M.; Cant, Andrew J. (May 2015). "The importance of vaccination and immunoglobulin treatment for patients with primary immunodeficiency diseases (PIDs) – World PI Week April 22–29, 2015: FORUM".European Journal of Immunology.45 (5):1285–1286.doi:10.1002/eji.201570054.PMID25952627.S2CID1922332.
^abJaneway, Charles A Jr.; Travers, Paul; Walport, Mark; Shlomchik, Mark J. (2001)."The Humoral Immune Response".Immunobiology: The Immune System in Health and Disease (5th ed.).Archived from the original on 2 January 2021. Retrieved18 April 2022.
^Grubbs, Hailey; Kahwaji, Chadi I. (January 2022).Physiology, Active Immunity. Treasure Island, FL: StatPearls Publishing.PMID29939682.Archived from the original on 12 November 2021. Retrieved18 April 2022.
^Dudley, Matthew Z; Halsey, Neal A; Omer, Saad B; Orenstein, Walter A; O'Leary, Sean T; Limaye, Rupali J; Salmon, Daniel A (May 2020). "The state of vaccine safety science: systematic reviews of the evidence".The Lancet Infectious Diseases.20 (5):e80 –e89.doi:10.1016/s1473-3099(20)30130-4.ISSN1473-3099.PMID32278359.S2CID215751248.
^Scott (April 2004)."Classifying Vaccines"(PDF).BioProcesses International:14–23.Archived(PDF) from the original on 12 December 2013. Retrieved9 January 2014.
^CDC (11 February 2020)."COVID-19 and Your Health".Centers for Disease Control and Prevention.Archived from the original on 3 March 2021. Retrieved21 December 2020.
^Anguille S, Smits EL, Lion E, van Tendeloo VF, Berneman ZN (June 2014). "Clinical use of dendritic cells for cancer therapy".The Lancet. Oncology.15 (7): e257–267.doi:10.1016/S1470-2045(13)70585-0.PMID24872109.
^Sutter RW, Kew OM, Cochi SL (2008). "Poliovirus vaccine-live". In Orenstein WA, Offit PA, Plotkin SA (eds.).Vaccines: Expert Consult (Vaccines (Plotkin)). W. B. Saunders. p. 650.ISBN978-1416036111.
^Kanesa-thasan N, Sun W, Kim-Ahn G, Van Albert S, Putnak JR, King A, Raengsakulsrach B, Christ-Schmidt H, Gilson K, Zahradnik JM, Vaughn DW, Innis BL, Saluzzo JF, Hoke CH (April 2001). "Safety and immunogenicity of attenuated dengue virus vaccines (Aventis Pasteur) in human volunteers".Vaccine.19 (23–24):3179–3188.CiteSeerX10.1.1.559.8311.doi:10.1016/S0264-410X(01)00020-2.PMID11312014.
^Sox, Harold C.; Liverman, Catharyn T.; Fulco, Carolyn E.; War, Institute of Medicine (US) Committee on Health Effects Associated with Exposures During the Gulf (2000).Vaccines. National Academies Press (US).Archived from the original on 16 November 2021. Retrieved3 May 2019.
^"Thimerosal in vaccines". Center for Biologics Evaluation and Research, U.S. Food and Drug Administration. 6 September 2007.Archived from the original on 6 January 2013. Retrieved1 October 2007.
^abCenters for Disease Control and Prevention (12 November 2020),U.S. Vaccine Names,archived from the original on 21 August 2021, retrieved21 August 2021.
^abCenters for Disease Control and Prevention (7 August 2018),Tetanus (Lockjaw) Vaccination,archived from the original on 16 May 2016, retrieved21 May 2016.
^"Vaccine Status Table".Red Book Online. American Academy of Pediatrics. 26 April 2011.Archived from the original on 27 December 2013. Retrieved9 January 2013.
^"HPV Vaccine Safety". Centers for Disease Control and Prevention (CDC). 20 December 2013.Archived from the original on 10 November 2009. Retrieved10 January 2014.
^abGomez, Phillip L.; Robinson, James M.; Rogalewicz, James (2008)."Chapter 4: Vaccine Manufacturing". In Plotkin, Stanley A.; Orenstein, Walter A.; Offit, Paul A. (eds.).Vaccines (5th ed.). New York: Saunders Elsevier. pp. 45–58.ISBN978-1-4377-2158-4.Archived from the original on 18 April 2023. Retrieved26 March 2021.
^abcdefPlotkin, Stanley A.; Orenstein, Walter A.; Offit, Paul A.; Edwards, Kathryn M. (2017).Vaccines. Elsevier.ISBN978-0-323-39301-0.
^Morein B, Hu KF, Abusugra I (June 2004). "Current status and potential application of ISCOMs in veterinary medicine".Advanced Drug Delivery Reviews.56 (10):1367–1382.doi:10.1016/j.addr.2004.02.004.PMID15191787.
^South African Institute for Medical Research (1929).Annual report [Jaarverslag]. South African Institute for Medical Research – Suid-Afrikaanse Instituut vir Mediese Navorsing.
^van Oirschot JT, Gielkens AL, Moormann RJ, Berns AJ (June 1990). "Marker vaccines, virus protein-specific antibody assays and the control of Aujeszky's disease".Veterinary Microbiology.23 (1–4):85–101.doi:10.1016/0378-1135(90)90139-M.PMID2169682.
^Kaashoek MJ, Moerman A, Madić J, Rijsewijk FA, Quak J, Gielkens AL, van Oirschot JT (April 1994). "A conventionally attenuated glycoprotein E-negative strain of bovine herpesvirus type 1 is an efficacious and safe vaccine".Vaccine.12 (5):439–444.doi:10.1016/0264-410X(94)90122-8.PMID8023552.
^Maas A, Meens J, Baltes N, Hennig-Pauka I, Gerlach GF (November 2006). "Development of a DIVA subunit vaccine against Actinobacillus pleuropneumoniae infection".Vaccine.24 (49–50):7226–7237.doi:10.1016/j.vaccine.2006.06.047.PMID17027123.
^Needham, Joseph (2000).Science and Civilisation in China: Volume 6, Biology and Biological Technology, Part 6, Medicine. Cambridge University Press. p. 154.ISBN978-0-521-63262-1.
^Van Sant JE (2008). "The Vaccinators: Smallpox, Medical Knowledge, and the 'Opening' of Japan".J Hist Med Allied Sci.63 (2):276–279.doi:10.1093/jhmas/jrn014.
^Sala F, Manuela Rigano M, Barbante A, Basso B, Walmsley AM, Castiglione S (January 2003). "Vaccine antigen production in transgenic plants: strategies, gene constructs and perspectives".Vaccine.21 (7–8):803–808.doi:10.1016/s0264-410x(02)00603-5.PMID12531364.
^abLeonhardt, David (11 March 2024)."The Fourth Anniversary of the Covid Pandemic".The New York Times.Archived from the original on 11 March 2024. "Data excludes Alaska. Sources: C.D.C. Wonder; Edison Research. (Chart) By The New York Times. Source credits chart to Ashley Wu.
^Smith, MJ (November 2015). "Promoting Vaccine Confidence".Infectious Disease Clinics of North America (Review).29 (4):759–69.doi:10.1016/j.idc.2015.07.004.PMID26337737.
^Larson, HJ; Jarrett, C; Eckersberger, E; Smith, DM; Paterson, P (April 2014). "Understanding vaccine hesitancy around vaccines and vaccination from a global perspective: a systematic review of published literature, 2007–2012".Vaccine.32 (19):2150–59.doi:10.1016/j.vaccine.2014.01.081.PMID24598724.
^Poland GA, Jacobson RM (January 2011). "The age-old struggle against the antivaccinationists".The New England Journal of Medicine.364 (2):97–99.doi:10.1056/NEJMp1010594.PMID21226573.S2CID39229852.
This website was highlighted byGenetic Engineering & Biotechnology News in its "Best of the Web" section in January 2015. See:"The History of Vaccines". Best of the Web.Genetic Engineering & Biotechnology News. Vol. 35, no. 2. 15 January 2015. p. 38.
