Science & Technology Policy BriefVaccinesVaccination is a critical measure for safeguarding public health and is an essential element of healthcare programs worldwide. This brief outlines the science behind vaccines, their role in public health, vaccine development process, and related concerns.SummaryVaccines simulate some features of a low-intensity infection to prepare the immune system to respond to future infections.Mass vaccination breaks the chain of transmission, protecting not just the vaccinated, but also a wider populace.Improvement in understanding of disease-determinants has led to development of new vaccine design approaches and technologies.Effective vaccine design needs to account for the evolution of the pathogen and variability in the immune response.Continuous surveillance and research are critical to vaccine development.IntroductionVaccines are critical in preventing infectious diseases caused by microorganisms such as bacteria and viruses.  Some diseases are highly transmissible, causing public health emergencies, such as the Measles outbreak in Maharashtra in 2022, the COVID-19 pandemic in 2020, the Japanese Encephalitis outbreak in Bihar in 2019, and the Nipah virus outbreak in Kerala in 2018.[1],[2],[3],[4]The impact is seen in terms of loss of life, significant expenses on treatments, strained health systems, and negative economic consequences.Vaccines are an important feature of public health policy.  Vaccines have helped eradicate diseases such as smallpox (across the globe) and polio (across many countries).  As per a Lancet study, vaccination against COVID-19 is estimated to have lowered the death toll by two-thirds at the global level in 2021.[5]Vaccine and the Immune SystemMicroorganisms such as viruses and bacteria can be several times smaller than the human cells.[6]This means that these pathogens (disease causing microorganisms) can enter the human body and replicate themselves within a human cell or outside of a cell.   These may enter the body through air, water, skin cracks, and the bloodstream through vectors such as mosquitoes.[7]The presence of a pathogen inside a healthy human body and its replication inside the host is called infection.[8]If an infection cannot be controlled, damage to the body starts resulting in illness or disease.  The human body has an elaborate mechanism, called the immune system, to fight infections.  The immune system has three key properties:[9],[10]Distinction between self and foreign: It possesses the ability to recognise and destroy foreign microorganisms such as bacteria and viruses, while leaving its own cells unharmed.Memory: After it eliminates a pathogen when encountered for the first time, the system remembers the pathogen and keeps itself ready to mount a rapid and effective response for subsequent infections.Specificity: The response is specific to the pathogen with different infections resulting in different responses.Vaccines leverage the above properties to prevent an infection from developing into a disease.9Vaccines introduce a pathogen in whole or in part to the body of a healthy person.[11]This triggers the immune system to prepare a response and build memory to fight any future infections effectively.Mass vaccination protects the vaccinated as well as unvaccinated.[12]When a sufficiently large proportion of the population develops immunity either through vaccination or through prior infection, the chances of any infected person coming into contact with a person without immunity is low.  Consequently, the pathogen has difficulty in finding susceptible hosts in the population, thus reducing the degree of transmission.  This is referred to as herd immunity.12This makes vaccination an effective measure for protecting the population at large against some infectious diseases.Figure1: Herd ImmunityImmune ResponseImprovements in the understanding of the immune response to a pathogen has been key to development of vaccines.  There are two key types of immune responses against a pathogen.[13],[14]These work together to prevent an infection from developing into a disease or illness.[15],[16],[17]Innate immune responseis the first line of defence against an invading pathogen.14,16This response is immediate and non-specific, i.e., the response does not differ based on the type of the pathogen.  Innate response is a culmination of a variety of cells performing certain specific functions.   These cells populate all tissues and blood in a human body.17They have receptors which can identify a molecular pattern associated with a pathogen or an infected cell.10,16These patterns are distinct from uninfected human cells, resulting in identification of foreign entities.There are cells called natural killer cells which identify infected cells using the above mechanism, and give them instructions to self-destruct in a controlled manner.13Two other types of cells, called macrophages and neutrophils, can identify, and ingest a pathogen or a dead human cell.  Thus, these cells eliminate pathogens, which have not yet entered a human cell, or the ones killed by the natural killer cells.  Macrophages, as well as another set of cells called dendritic cells, release cytokines (type of proteins which act as messengers to the different parts of immune system) and other chemicals to cause inflammation.17Inflammation results in more of these cells to reach the site of an infection, and intensify the immune response.16,17If a pathogen invades in large numbers, the innate immune response might not be enough.17Certain pathogens have also evolved to have the ability to evade the innate response.10,16This is where another type of response called adaptive immune response comes into picture, which complements the innate immune response.15Adaptive immune response:This response mechanism identifies the pathogen and develops a special counter to it.   Two sub-types of White Blood Cells, B-cells, and T-cells, play a central role in the adaptive immune response.[18],[19]These cells can identify antigen, which are substances such as protein or complex sugar molecules found on the surface of pathogens.  The body produces a large number of B-cells and T-cells, with diversified receptors to identify different antigen.13The number of different types of receptors is estimated to be of the order of a billion.17If an antigen were to be considered to be a lock, by producing a wide variety of B-cells and T-cells with different receptors, the body is producing a wide variety of keys hoping that one of these might be able to open the lock.Once presented with an antigen, those B-cells and T-cells, which have receptors that can recognise that antigen, clone themselves rapidly to increase their number for mounting the response.16,17Certain cells from the innate response such as macrophages and dendritic cells help T-cells identify the antigen.11,17B-cells differentiate and proliferate into short lived Plasma cells which produce antibodies.[20],[21]Antibodies are a kind of protein which specifically bind to the antigen.  This binding marks the pathogen for ingestion and destruction by macrophages and certain other cells.17T-cells identify the infected cells, they either help such cells to kill pathogens inside them or eliminate them in a similar manner as the killer cells of the innate response.13Some B-cells differentiate into long-lived plasma cells and memory cells.[22]Memory B-cells persist for longer.  They have a 10-100 times higher antibody production capability on antigen exposure.16,17T-cells also differentiate into memory cells with a relatively longer lifespan, providing capability for a rapid response on subsequent infections.[23]The adaptive immune response can take days to develop, increasing the chances of an infection developing into a disease.9As mentioned earlier, vaccines prevent this by simulating a low-intensity infection to stimulate the adaptive immune response in advance, thereby building immune memory.   Vaccines target adaptive immune response to fight against the pathogen.  Immune response may vary with factors such as age, genetics, and environmental factors.19Types of VaccinesVaccines aim to stimulate the immune system by exposing it to a pathogen or a part of it.[24]This can be achieved by administering: (i) whole pathogen (weakened or dead), (ii) sub-unit of a pathogen, i.e., protein or carbohydrates found on its surface, or (iii) genetic material such as DNA or RNA to provide instruction to human cells to synthesise protein associated with the pathogen.  Proteins or carbohydrates derived from the pathogen can also trigger immune response similar to introduction of a full pathogen in the human body.[25],[26],[27],[28],[29],[30],[31]Table1: Common vaccine typesTypeAdministered MaterialExamplesLive AttenuatedAlive but weakened pathogenBCG, RotavirusInactivatedDead pathogenPolio, COVAXINSub-UnitProtein or carbohydrate on surface of pathogenHPV, Tetanus, NovovaxDNADNA with information for sythensising protein associated with targeted pathogenZydus Cadila COVID VaccinemRNARNA with instruction for synthesising protein associated with targeted pathogenPfizer and Moderna COVID vaccinesViral VectoredA weakened, generally non replicating live virus carrying genetic material of targeted pathogenAstraZeneca COVID Vaccine, Ervebo (Ebola Vaccine)Sources: Types of Vaccines, University of Oxford; PRS.DNA, mRNA, and viral vectored vaccines are relatively newer approaches to vaccine development, and are categorised asplatform-based technologies.24In these, a standardised platform is used to deliver genetic material inside human cells to stimulate the immune response.[32]Genetic information carried by these delivery platforms can easily be modified, allowing for quicker development and adaptation of vaccines against the evolution of the pathogen.[33]These methods are limited to use against protein-based antigens as the body can only synthesise proteins from an external instruction, and will not work against bacteria, which are carbohydrate-based.[34]TrialsAs vaccines are given to healthy persons, the efficacy as well as safety of vaccines must be demonstrated.  These aspects are tested in phased trials.  Efficacy is defined as the observed reduction in incidence (number of cases of infection) in vaccinated persons as compared to the same in those unvaccinated.[35]If the incidence in an unvaccinated group of 500 persons is 100, and that in a vaccinated group of 500 persons is 40, then the incidence reduction rate is 60%, which is the efficacy.  Regulatory authorities across the globe typically require a proven efficacy of more than 50% to approve a vaccine.[36]Table2: Clinical Trials for Vaccines[37]PhaseSample SizePurposeI5 to 50Assessing safety, immune response, optimising dose scheduleII25 to 1,000Expanding study for safety, immune response, and optimising dose scheduleIII100 to 10,000Assessing efficacy and safety at a bigger scaleIV100,000 to millionsAssessing the side effects caused over time by a vaccine after approvalSources: Vaccines and Immunization, CDC; PRS.Box 1: Vaccines against COVID-19The COVID-19 pandemic was caused by a member of the SARS virus family called SARS-CoV-2.1Herd immunity achieved via mass vaccination was seen as a way out of pandemic.  This led to extensive government programs funding the research and development of vaccines globally.[38]The first vaccine was approved by WHO in December 2020, one year into the pandemic.[39]Adoption of COVID-19 vaccines was expedited through emergency use authorisation, an accelerated process for regulatory approval.As on May 31, 2023, India has recorded 4.5 crore COVID-19 cases with 5.3 lakh deaths.[40]A fully public-funded mass vaccination programme against COVID-19 has been running in India since January 2021.[41]The program is estimated to have cost Rs 36,405 crore over three years.[42]The COVID Suraksha Mission, with an estimated cost of about Rs 900 crore, was launched in November 2020 to accelerate the development of COVID-19 vaccines domestically.[43]As of January 2023, this program has yielded four approved COVID-19 vaccines.[44]Early-stage studies on humansBefore a vaccine goes for clinical trials, animal trials are done to study response to a vaccine.37These trials however have certain limitations.[45]The host-parasite interaction in animals may not be similar to that in humans.  Clinical trials are also cost and time intensive.  Controlled Human Infection Model Studies (CHIM) are expected to aid current mechanisms to address these issues.45In CHIM studies, the subject is intentionally infected with the pathogen under a controlled environment.[46]These studies help in narrowing down a suitable vaccine candidate and speeding up vaccine development.45They can also help in developing vaccines particular to a population as efficacy changes with genetic complexities, environmental factors, and nutritional status.46While these studies may be useful, they present ethical concerns as it involves infecting healthy people at an experimental stage.[47]Currently, India does not have any framework for CHIM studies.46SurveillanceAs pathogens may keep evolving and evade the vaccine induced immune response, surveillance of variants and mutations becomes critical.  From a safety perspective, it is also critical to continue monitoring for any adverse events (any minor or major illness after vaccination).  This makes surveillance systems an essential pillar of the public health system.[48]A 2020 report by NITI Aayog observed that India’s surveillance system is not well integrated, with different monitoring agencies working in silos.[49]As a result, the data collected is patchy.  The report also observed that there is a dearth of human resource for public health surveillance.49Another challenge is increasing incidences of zoonotic diseases, i.e., diseases jumping from animals to humans.  As per WHO, 75% of emerging infections in humans are zoonotic in nature.[50]Hence, strengthening disease surveillance in animals has the added advantage of protecting humankind through the early detection, prevention, and control of zoonotic diseases.[51]In 2021, the Department of Biotechnology of the central government had launched One Health Mission to monitor the prevalence of zoonotic diseases.[52]Status of Vaccination in IndiaThe central government-funded universal immunisation programme in India provides children with free vaccines against 12 diseases.[53],[54]The percentage of children who got all vaccines under this program has significantly improved over the years (referred to as immunisation coverage).  The coverage has increased from 35% in 1992-93 to 76% in 2019-21, which is well short of achieving universal coverage.[55]There is also significant variation across states.  The North-eastern states barring Sikkim, fare poorly, with Nagaland having 58% coverage and coverage in others in the range of 60-70%.[56]Certain large states including Uttar Pradesh, Maharashtra, and Bihar have their coverage around 70%, while the large states with highest coverage are Odisha (91%), Tamil Nadu (89%), and West Bengal (88%).[57]Table 3: Adoption of vaccines in India[58],[59],[60]CategoryDiseasesVaccines covered under the Universal Immunisation ProgramNationally: Diphtheria, Pertussis, Tetanus, Polio, Measles, Rubella, severe Tuberculosis, Hepatitis B, Meningitis, Pneumonia, Rotavirus Diarrhoea, Pneumococcal PneumoniaSub-Nationally: Japanese EncephalitisVaccines approved in India, but not covered under government programsHPV, Hepatitis A, Typhoid, Rabies, Influenza, Herpes zoster, Varicella zosterVaccines approved by WHO, but not approved in IndiaDengue (under phase 3 trials in India)Prevalent diseases in India for which no vaccines are approved globallyTuberculosis in adults, AIDS, Hepatitis C, Malaria variety dominant in IndiaSources: National Health Mission, World Health Organisation; PRS.Developing vaccines for IndiaIndia has a significant presence in the vaccine manufacturing ecosystem through its private players.  In 2021, Serum Institute and Bharat Biotech of India were amongst the top 10 manufacturers of vaccines by volume (excluding COVID-19 vaccines), with 20% and 7% share in the global market, respectively.[61]Existence of these manufacturing capabilities within the country helped India in securing vaccine supplies for COVID-19.  However, their share by value in the global market is much lower (< 2% in 2021).61Box 2: New Frontiers in Vaccine Technology[62],[63]Universal Vaccines:These aim to target common elements shared across multiple strains or species of pathogens, to provide broader protection against a family of pathogens, such as flu virus or coronavirus families.Therapeutic Vaccines:These aim to treat instead of prevent diseases such as cancer or Alzheimer’s disease.Personalised Vaccines: These aim to customise vaccine to factor an individual’s genetics to improve immune response.This may indicate limited presence and capability in developing newer and higher-value vaccines.Vaccine development is cost intensive as research and development (R&D) requires sophisticated infrastructure and a long timeframe due to regulatory requirements.61,[64]There may not be a guarantee of a vaccine candidate reaching the market or assured procurement from government.These uncertainties limit the investments by the private sector towards R&D.  Development of a relatively higher number of vaccines for COVID-19 were spurred by government incentives for R&D as well as assured procurement globally.35There could be diseases prevalent only in India, due to environment and other factors.   Other countries may not have the incentive to invest in vaccines for them.  WHO (2022) observed that diseases associated with markets of little commercial value have remained neglected, have seen suboptimal investment, and have only a few products in the development pipeline.61These include diseases referred to asneglected tropical diseases.[65]Some of these diseases such as dengue and lymphatic filariasis are prevalent in India.  Hence, India may need a sustained directed effort towards R&D in vaccines.Public funding may also become necessary to widely administer vaccines against certain diseases.  Given limited resources and a range of diseases to protect against, decisions such as funds for R&D or mass vaccination need to take various factors into account.  These could include susceptibility, transmissibility, disease burden, and geographical spread.   These may help in deciding the scale of mass vaccination.[66]For example, Polio vaccine is given across India, while Japanese Encephalitis is given only in some states.54The Rabies vaccine is given only to people bitten by a rabid animal and not everyone.[67]The trade-off between treatment and the cost of vaccination and morbidity of a disease helps government decide roll out of a vaccine.  Chickenpox has a vaccine but vaccination is usually not recommended.[68]There are diseases such as hepatitis-A and cervical cancer, for which vaccines are available but not given freely through the public health system.[69][1]“State records 2692 measles cases in 2022, highest in country”, The Indian Express, March 20, 2023,https://indianexpress.com/article/cities/mumbai/state-records-2692-measles-cases-in-2022-highest-in-country-8507104/.[2]“COVID-19 Pandemic”, World Health Organisation, (as accessed on May 5, 2023),https://www.who.int/europe/emergencies/situations/covid-19.[3]“Centre to form permanent expert group to tackle AES outbreak in Bihar”, Hindu Business Line, December 6, 2021,https://www.thehindubusinessline.com/news/national/centre-to-form-permanent-expert-group-to-tackle-aes-outbreak-in-bihar/article28066547.ece.[4]“Nipah Virus Outbreak in Kerala”, World Health Organisation, (as accessed on May 5, 2023),https://www.who.int/southeastasia/outbreaks-and-emergencies/health-emergency-information-risk-assessment/surveillance-and-risk-assessment/nipah-virus-outbreak-in-kerala.[5]“Global impact of the first year of COVID-19 vaccination: a mathematical modelling study”, The Lancet, June 23, 2022https://www.thelancet.com/journals/laninf/article/PIIS1473-3099(22)00320-6/fulltext#articleInformation.[6]“Microbe Size”, LibreTexts Biology, (as accessed on May 18, 2023),https://bio.libretexts.org/Bookshelves/Microbiology/Microbiology_(Boundless)/03%3A_Microscopy/3.01%3A_Looking_at_Microbes/3.1A%3A_Microbe_Size#:~:text=Even%20in%20comparison%20to%20animal,other%20microbes%20such%20as%20bacteria.[7]“What You Need to Know About Infectious Disease”, National Library of Medicine, (as accessed on May 18, 2023),https://www.ncbi.nlm.nih.gov/books/NBK209710/.[8]“NCI Dictionary of Cancer Terms”, National Cancer Institute, (as accessed on May 18, 2023),https://www.cancer.gov/publications/dictionaries/cancer-terms/def/infection.[9]Margolick, J., Markham, R., & Scott, A. (2022). The Immune System and Host Défense Against Infections. In C.M. Williams, Infectious Disease Epidemiology: Theory and Practice (3rded., pp. 253). Jones & Bartlett Learning.[10]Parija, S.C. (2012), Immunity, Textbook of Microbiology & Immunology (2nded., pp. 85), Elsevier.[11]“Receptors of the innate immune system”, National Library of Medicine, (as accessed on May 19, 2023),https://www.ncbi.nlm.nih.gov/books/NBK27129/.[12]“Immunization”, U.S. Department of Health and Human Services, (as accessed on May 18, 2023),https://www.hhs.gov/immunization/basics/work/protection/index.html.[13]Pollard, A. J., & Bijker, E. M. (2021). A guide to vaccinology: from basic principles to new developments.Nature reviews. Immunology,21(2), 83–100.https://doi.org/10.1038/s41577-020-00479-7.[14]“The innate and adaptive immune systems”, National Library of Medicine, (as accessed on May 19, 2023),https://www.ncbi.nlm.nih.gov/books/NBK279396/.[15]“The Adaptive Immune System”, National Library of Medicine, (as accessed on May 19, 2023),https://www.ncbi.nlm.nih.gov/books/NBK21070/.[16]Paniker, R. &et al.(2020b). Ananthnarayan and Paniker’s Textbook of Microbiology.[17]Pillai, S., Abbas, K. & Lichtman, A. (2019b). Basic Immunology 6thEdition South Asia Edition.[18]“Lymphocytes”, Cleveland Clinic, (as accessed on May 2, 2023),https://my.clevelandclinic.org/health/body/23342-lymphocytes.[19]‘Understanding Immunological Memory’, American Society for Microbiology, May 11, 2023,https://asm.org/Articles/2023/May/Understanding-Immunological-Memory.[20]Kealy L. & Good-Jacobson K., Advances in understanding the formation and fate of B-cell memory in response to immunization or infection,Oxford Open Immunology, Volume 2, Issue 1, 2021, iqab018,https://doi.org/10.1093/oxfimm/iqab018.[21]Akkaya, M., Kwak, K. & Pierce, S.K. B cell memory: building two walls of protection against pathogens.Nat Rev Immunol20, 229–238 (2020).https://doi.org/10.1038/s41577-019-0244-2.[22]Ratajczak, W., Niedźwiedzka-Rystwej, P., Tokarz-Deptuła, B., & Deptuła, W. (2018). Immunological memory cells.Central-European journal of immunology,43(2), 194–203.https://doi.org/10.5114/ceji.2018.77390.[23]Anderson, S. M., Hannum, L. G., & Shlomchik, M. J. (2006). Memory B cell survival and function in the absence of secreted antibody and immune complexes on follicular dendritic cells.Journal of immunology (Baltimore, Md.: 1950),176(8), 4515–4519.https://doi.org/10.4049/jimmunol.176.8.4515.[24]“Types of Vaccine”, University of Oxford, (as accessed on April 28, 2023),https://vaccineknowledge.ox.ac.uk/types-of-vaccine.[25]“Nature Milestones in Vaccines”, Nature, (as accessed on May 5, 2023),https://www.nature.com/immersive/d42859-020-00005-8/index.html.[26]“Vaccine Types”, US Department of Health and Human Services, (as accessed on May 5, 2023),https://www.hhs.gov/immunization/basics/types/index.html.[27]“Principles of Vaccination”, Centre for Disease Control and Prevention,https://www.cdc.gov/vaccines/pubs/pinkbook/downloads/prinvac.pdf.[28]“Covaxin-India’s first indigenous vaccine”, Bharat Biotech, (as accessed on May 5, 2023),https://www.bharatbiotech.com/covaxin.html#:~:text=The%20vaccine%20is%20developed%20using,Vero%20Cell%20derived%20platform%20technology.[29]“The Different Types of COVID-19 Vaccines”, World Health Organisations (as accessed on May 5, 2023),https://www.who.int/news-room/feature-stories/detail/the-race-for-a-covid-19-vaccine-explained.[30]“How Vaccines Work”, US Centre for Disease Control and Prevention, (as accessed on May 3, 2023),https://www.cdc.gov/coronavirus/2019-ncov/vaccines/different-vaccines/how-they-work.html.[31]“The Oxford/AstraZeneca (ChAdOx1-S [recombinant] vaccine) COVID-19 vaccine: what you need to know”, World Health Organisation, (as accessed on May 5, 2023),https://www.who.int/news-room/feature-stories/detail/the-oxford-astrazeneca-covid-19-vaccine-what-you-need-to-know.[32]“Next-generation vaccine platforms for COVID-19”, Nature, July 23, 2020,https://doi.org/10.1038/s41563-020-0746-0.[33]“What Has the Pandemic Taught Us About Vaccines?”, Quanta Magazine, April 5, 2023,https://www.quantamagazine.org/what-has-the-pandemic-taught-us-about-vaccines-20230405/.[34]“Genetic Code”, National Human Genome Research Institute, (as accessed on May 21, 2023),https://www.genome.gov/genetics-glossary/Genetic-Code.[35]“Vaccine efficacy, effectiveness, and protection”, World Health Organisation, (as accessed on April 28, 2023),https://www.who.int/news-room/feature-stories/detail/vaccine-efficacy-effectiveness-and-protection.[36]“Emergency Use Authorization”, US Food and Drug Administration, (as accessed on May 3, 2023),https://www.fda.gov/emergency-preparedness-and-response/mcm-legal-regulatory-and-policy-framework/emergency-use-authorization.[37]Milligan, G. N., & Barrett, A. D. T. (2015).Vaccinology: An Essential Guide. John Wiley & Sons.[38]“Mapping of long-term Public and Private Investments in the Development of COVID-19 Vaccines”, Policy Department for Economic, Scientific and Quality of Life Policies,https://www.europarl.europa.eu/RegData/etudes/STUD/2023/740072/IPOL_STU(2023)740072_EN.pdf.[39]“WHO issues its first emergency use validation for a COVID-19 vaccine and emphasizes need for equitable global access”, World Health Organisation, (as accessed on December 31, 2020),https://www.who.int/news/item/31-12-2020-who-issues-its-first-emergency-use-validation-for-a-covid-19-vaccine-and-emphasizes-need-for-equitable-global-access.[40]“WHO COVID-19 Dashboard India Page”, World Health Organisation, (as accessed on May 5, 2023),https://covid19.who.int/region/searo/country/in.[41]“India marks one year of COVID-19 vaccination”, World Health Organisation, January 17, 2022,https://www.who.int/india/news/feature-stories/detail/india-marks-one-year-of-covid-vaccination.[42]Demand No 42, Expenditure Budget, Union Budget 2023-24,https://www.indiabudget.gov.in/doc/eb/sbe42.pdf.[43]“DBT through Mission COVID Suraksha delivered four vaccines”, Press Information Bureau, Ministry of Science and Technology, January 27, 2023,https://www.pib.gov.in/PressReleasePage.aspx?PRID=1894167.[44]“Nature Milestones in Vaccines”, Nature, September 28, 2020,https://www.nature.com/immersive/d42859-020-00005-8/index.html.[45]“Controlled Human Infection Models: Promises and Concerns for India”, IndiaBioscience, September 18, 2023,https://indiabioscience.org/columns/indian-scenario/controlled-human-infection-models-promises-and-concerns-for-india.[46]Sekhar, A., & Kang, G. (2020). Human challenge trials in vaccine development.Seminars in immunology,50, 101429.https://doi.org/10.1016/j.smim.2020.101429.[47]WHO guidance on the ethical conduct of controlled human infection studies 2021, World Health Organisation,https://www.who.int/publications/i/item/9789240037816.[48]Rodrigues, C. M. C., & Plotkin, S. A. (2020). Impact of Vaccines; Health, Economic and Social Perspectives.Frontiers in microbiology,11, 1526.https://doi.org/10.3389/fmicb.2020.01526.[49]Vision 2035: Public Health Surveillance in India, NITI Aayog 2020,https://www.niti.gov.in/sites/default/files/2020-12/PHS_13_dec_web.pdf.[50]“Strengthening global health security at human-animal level”, World Health Organisation, (as accessed on May 5, 2023),https://www.who.int/activities/strengthening-global-health-security-at-the-human-animal-interface.[51]“Preventing emerging zoonoses”, UK Parliament, as accessed on May 10, 2023,https://post.parliament.uk/research-briefings/post-pn-0660/.[52]Annual Report 2022-23, Department of Biotechnology,https://dbtindia.gov.in/sites/default/files/Final%20Annual%20Report%20English%202022-23.pdf.[53]“National Immunisation Schedule”, Ministry of Health and Family Welfare, (as accessed on May 5, 2023),https://main.mohfw.gov.in/sites/default/files/Universal.pdf.[54]“Immunisation”, Website of National Health Mission, (as accessed on May 5, 2023),https://nhm.gov.in/index1.php?lang=1&level=2&sublinkid=824&lid=220.[55]Mission Intensified Indradhanush 4.0, Operational Guidelines 2022, Ministry of Health and Family Welfare,https://imi4.mohfw.gov.in/assets/document/operational/IMI4.0_oprational_guidelines.pdf.[56]National Family Health Survey-5 Phase I 2019-20, Ministry of Health and Family Welfare,https://main.mohfw.gov.in/sites/default/files/NFHS-5_Phase-I.pdf.[57]National Family Health Survey-5 Phase II 2020-21, Ministry of Health and Family Welfare,https://main.mohfw.gov.in/sites/default/files/NFHS-5_Phase-II_0.pdf.[58]“Immunisation, Vaccines and Biologicals”, World Health Organisation, (as accessed on May 15, 2023),https://www.who.int/teams/immunization-vaccines-and-biologicals/diseases.[59]“Vaccines”, Central Drugs Standard Control Organisation, (as accessed on May 15, 2023),https://cdsco.gov.in.[60]“Immunization, National Health Mission”, Ministry of Health, and Family Welfare, (as accessed on May 15, 2023),https://nhm.gov.in/index1.php?lang=1&level=2&sublinkid=824&lid=220.[61]Global Vaccine Market Report 2022, World Health Organisation,https://cdn.who.int/media/docs/default-source/immunization/vaccine_access_market/global-vaccine-market-report-2022-template-final2.pdf?sfvrsn=5e8ddbed_6&download=true.[62]Brisse, M., Vrba, S. M., Kirk, N., Liang, Y., & Ly, H. (2020). Emerging Concepts and Technologies in Vaccine Development.Frontiers in immunology,11, 583077.https://doi.org/10.3389/fimmu.2020.583077.[63]“Creating a versatile vaccine to take on Covid-19 in its many guises”, MIT News, March 9, 2023,https://news.mit.edu/2023/creating-versatile-vaccine-take-on-covid-19-0309.[64]Struck, MM (1996). Vaccine R&D success rates and development times.Nat Biotechnol14, 591–593.https://doi.org/10.1038/nbt0596-591.[65]“Neglected Tropical Diseases”, World Health Organisation  (as accessed on May 31, 2023),https://www.who.int/health-topics/neglected-tropical-diseases#tab=tab_1.[66]Framework for decision making: implementation of mass vaccination campaigns in the context of COVID-19, World Health Organisation, May 22, 2020,https://apps.who.int/iris/bitstream/handle/10665/332159/WHO-2019-nCoV-Framework_Mass_Vaccination-2020.1-eng.pdf.[67]“Vaccine Information Statement”, Centre for Disease Control and Prevention, (as accessed on May 20, 2023),https://www.cdc.gov/vaccines/hcp/vis/vis-statements/rabies.html.[68]“Comparing Natural and Vaccine Immunity”, Michigan government website, (as accessed on May 20, 2023),https://www.michigan.gov/-/media/Project/Websites/mdhhs/Adult-and-Childrens-Services/Children-and-Families/Immunization-Information/LHD/Waiver_Ed_Natural_Immunity.pdf?rev=ad5bf279bcae4bdca060d075be344480.[69]Verma, R., & Khanna, P. (2012). Hepatitis A vaccine should receive priority in National Immunization Schedule in India.Human vaccines & immunotherapeutics,8(8), 1132–1134.https://doi.org/10.4161/hv.20475.DISCLAIMER: This document is being furnished to you for your information.  You may choose to reproduce or redistribute this report for non-commercial purposes in part or in full to any other person with due acknowledgement of PRS Legislative Research (“PRS”).  The opinions expressed herein are entirely those of the author(s).   PRS makes every effort to use reliable and comprehensive information, but PRS does not represent that the contents of the report are accurate or complete.  PRS is an independent, not-for-profit group.  This document has been prepared without regard to the objectives or opinions of those who may receive it.
Science & Technology Policy Brief : Vaccines