Vaccines and Immunity
Innate and adaptive immunity, antibodies, types of immunity and vaccines, the Universal Immunization Programme, Mission Indradhanush and the 2026 HPV drive, for CGPSC.
Prerequisites
- Cell and Human Body Systems — white blood cells and the lymphatic organs.
- Communicable Diseases and Health Programmes — the diseases vaccines prevent.
The Hook: The MCP Card and the Cold Box
On its fixed immunisation day, the ANM arrives at a village anganwadi in Kanker with a blue vaccine carrier full of ice packs. Mothers bring their babies and the Mother and Child Protection card (मातृ एवं शिशु सुरक्षा कार्ड). A six-week-old gets the pentavalent shot and oral drops; a nine-month-old gets the measles-rubella vaccine. Since early 2026, 14-year-old girls in the same block are being offered a single dose of HPV vaccine against cervical cancer.
Why are some vaccines drops and others injections? Why must they stay between 2 °C and 8 °C? How does a single shot protect for years? This page answers these questions.
Why it matters: Prelims asks about types of immunity, antibodies, vaccine types and UIP facts. Mains GS-II asks how vaccines work, India’s immunisation achievements and gaps, and vaccine hesitancy. Recent events (COVID-19 vaccines, the 2026 HPV campaign) make this a current-affairs favourite.
The Immune System (प्रतिरक्षा तंत्र)
Immunity is the body’s ability to resist disease-causing organisms. It has two layers.
| Feature | Innate (non-specific) immunity (सहज प्रतिरक्षा) | Adaptive / acquired (specific) immunity (उपार्जित प्रतिरक्षा) |
|---|---|---|
| Present | From birth | Develops after exposure to a pathogen or vaccine |
| Specificity | Same response to all invaders | Specific to each antigen |
| Speed | Immediate | Slower the first time; faster and stronger the second time |
| Memory | No | Yes (memory cells): the basis of vaccination |
| Examples | Physical barriers: skin, mucus, cilia. Chemical: stomach acid, tears and saliva (lysozyme). Cellular: neutrophils and macrophages (phagocytes), natural killer cells. Inflammation, fever, interferons (against viruses) | B lymphocytes (antibodies) and T lymphocytes (cell-mediated) |
The two arms of adaptive immunity
| Arm | Cells | How it works |
|---|---|---|
| Humoral (antibody-mediated) | B cells, which become plasma cells | Release antibodies into blood and body fluids that neutralise germs and toxins |
| Cell-mediated | T cells (mature in the thymus) | Helper T cells coordinate the response; cytotoxic (killer) T cells destroy infected and cancer cells. Cell-mediated immunity is also why transplanted organs are rejected |
- An antigen is any molecule the immune system recognises as foreign. An antibody (प्रतिपिंड) is a Y-shaped protein (immunoglobulin) made in response.
- Primary lymphoid organs (where lymphocytes form and mature): bone marrow and thymus. Secondary: spleen, lymph nodes, tonsils, Peyer’s patches of the gut.
The five classes of antibodies
| Class | Key fact |
|---|---|
| IgG | Most abundant; the only one that crosses the placenta (protects the newborn) |
| IgA | In secretions: saliva, tears, colostrum (first breast milk) |
| IgM | First antibody made in an infection; largest (pentamer) |
| IgE | Allergies (triggers histamine release from mast cells) and worm infections |
| IgD | On the surface of B cells; role in activating them |
Mnemonic: “GAMED”.
Types of Acquired Immunity
| Active (body makes its own antibodies; slow, long-lasting, memory) | Passive (ready-made antibodies given; immediate, short-lived, no memory) | |
|---|---|---|
| Natural | Recovering from an infection (e.g. chickenpox) | Mother’s IgG across the placenta; IgA in colostrum |
| Artificial | Vaccination | Antiserum / immunoglobulin injections: anti-tetanus serum, anti-snake venom, rabies immunoglobulin, monoclonal antibodies |
When immunity goes wrong
| Disorder | What happens | Examples |
|---|---|---|
| Allergy (hypersensitivity) | Over-reaction to harmless substances (allergens); IgE and histamine | Hay fever, asthma, food allergy. Treated with antihistamines, steroids; severe reaction (anaphylaxis) needs adrenaline |
| Autoimmune disease | Immune system attacks the body’s own cells | Rheumatoid arthritis, type 1 diabetes, multiple sclerosis |
| Immunodeficiency | Immune system too weak | AIDS (HIV destroys helper T / CD4 cells), inborn disorders |
Vaccines (टीका): How They Work
A vaccine exposes the immune system to a harmless form or part of a pathogen (antigen). The body makes antibodies and, crucially, memory B and T cells. When the real pathogen arrives, the memory cells mount a fast, strong secondary response before disease sets in.
Herd immunity (सामूहिक प्रतिरक्षा): when enough people are immune, the pathogen cannot find new hosts, which protects people who cannot be vaccinated (newborns, the very ill). For a highly infectious disease like measles, roughly 95% coverage is needed.
Milestones
| Year | Milestone |
|---|---|
| 1796 | Edward Jenner uses cowpox to protect against smallpox. The word “vaccine” comes from Latin vacca (cow) |
| 1880s | Louis Pasteur: vaccines against chicken cholera and anthrax, and the rabies vaccine (1885). Called the father of immunology (with Jenner) |
| 1921 | BCG (Bacillus Calmette–Guérin) first given, against TB |
| 1955 / early 1960s | Salk injectable inactivated polio vaccine (IPV) / Sabin oral polio vaccine (OPV) |
| 1980 | Smallpox declared eradicated worldwide |
| 2020–21 | First mRNA vaccines (COVID-19). India’s COVID-19 vaccination drive began on 16 January 2021 |
Types of vaccines
| Type | What is inside | Examples |
|---|---|---|
| Live attenuated | Weakened live pathogen; strong, long immunity; not for the severely immunocompromised | BCG, OPV, measles-rubella (MR), rotavirus, chickenpox, yellow fever |
| Inactivated (killed) | Whole pathogen killed by heat or chemicals | IPV, rabies, hepatitis A, Covaxin |
| Toxoid | Inactivated toxin | Tetanus, diphtheria (Td) |
| Subunit / recombinant / virus-like particle | Only a protein or part of the pathogen, often made by recombinant DNA technology | Hepatitis B (first recombinant vaccine), HPV, Corbevax (COVID-19) |
| Conjugate | Sugar coat of a bacterium linked to a protein so infants respond well | Hib, pneumococcal (PCV), typhoid conjugate |
| Viral vector | Harmless virus carries a gene for the antigen | Covishield (Oxford–AstraZeneca design, made by the Serum Institute of India) |
| Nucleic acid | Genetic instructions (mRNA or DNA) so our cells make the antigen | mRNA: Pfizer–BioNTech, Moderna. DNA: ZyCoV-D (Zydus, approved in India in 2021), the world’s first DNA vaccine for humans |
- Covishield: viral vector; Serum Institute of India, Pune.
- Covaxin: inactivated whole virus; Bharat Biotech (Hyderabad) with ICMR–National Institute of Virology.
- ZyCoV-D: plasmid DNA vaccine, needle-free applicator; Zydus.
- Corbevax: protein subunit; Biological E. India’s vaccination drive used the Co-WIN digital platform for registration and certificates.
Cold chain: most vaccines must be kept at +2 °C to +8 °C from factory to child. The Vaccine Vial Monitor (VVM), a heat-sensitive label, shows if a vial has been exposed to too much heat. India tracks vaccine stocks and storage temperatures with the eVIN (Electronic Vaccine Intelligence Network, 2015).
India’s Immunisation Programme
| Programme | Year | Key point |
|---|---|---|
| Expanded Programme on Immunization (EPI) | 1978 | Forerunner |
| Universal Immunization Programme (UIP) | 1985 | Free vaccines for all children and pregnant women; one of the largest in the world |
| Pulse Polio | 1995 | Mass OPV campaigns. National Vaccination Day: 16 March (first Pulse Polio round, 1995) |
| Mission Indradhanush | Launched 25 December 2014 | Catch-up drive for unvaccinated and partly vaccinated children and pregnant women; Intensified Mission Indradhanush (IMI) rounds followed |
| U-WIN | Rolled out nationally in 2024 | Digital registry of every vaccination under UIP (successor to the Co-WIN idea) |
| National HPV vaccination campaign | Launched 28 February 2026, Ajmer (Rajasthan) | Single dose of the quadrivalent Gardasil-4 free for girls aged 14 at government facilities, against cervical cancer |
Diseases covered by UIP (as of 2026)
The Health Ministry describes UIP as covering 12 vaccine-preventable diseases:
| Coverage | Diseases |
|---|---|
| Nationally (9) | Diphtheria, pertussis (whooping cough), tetanus, polio, measles, rubella, severe childhood tuberculosis (BCG), hepatitis B, Haemophilus influenzae type b (Hib) meningitis and pneumonia |
| Sub-nationally (3) | Rotavirus diarrhoea, pneumococcal pneumonia, Japanese encephalitis (in endemic districts) |
| Added in 2026 | HPV for 14-year-old girls (national campaign) |
Pentavalent vaccine = DPT + hepatitis B + Hib in one shot (at 6, 10 and 14 weeks). Other key doses: BCG, OPV-0 and hepatitis B birth dose at birth; MR at 9–12 months and 16–24 months; Td for adolescents and pregnant women (protects the newborn from tetanus).
Coverage: government data (March 2026) put full immunisation coverage at about 98% in January 2026, up from 62% in 2015. NFHS-5 (2019–21), a household survey, had found 76.4% of children aged 12–23 months fully vaccinated. Survey and administrative figures differ, so always quote the source.
Vaccine institutes worth knowing
| Institute | Place |
|---|---|
| Serum Institute of India (private; one of the world’s largest vaccine makers by doses) | Pune |
| Bharat Biotech (Covaxin, Rotavac) | Hyderabad |
| Central Research Institute | Kasauli (Himachal Pradesh) |
| Pasteur Institute of India | Coonoor (Tamil Nadu) |
| ICMR–National Institute of Virology | Pune |
Analysis for Mains: Achievements, Gaps, Hesitancy
Achievements: polio-free certification (2014), maternal and neonatal tetanus elimination (2015), new vaccines added (rotavirus, PCV, MR, HPV), indigenous vaccines (Rotavac, Covaxin, ZyCoV-D, Cervavac), over two billion COVID-19 doses delivered with a digital backbone (Co-WIN, now U-WIN), and India’s role as a supplier of vaccines to the world.
Gaps:
- Zero-dose and partly vaccinated children in urban slums, migrant families and remote tribal hamlets.
- Cold-chain and access problems in forested, conflict-affected areas such as southern Chhattisgarh.
- Vaccine hesitancy: rumours, fear of side effects, mistrust; the HPV vaccine faces myths about fertility.
- Data gaps: administrative coverage often runs higher than survey coverage.
Way forward: use ASHAs and mitanins and local leaders to counter myths; due lists and reminders through U-WIN; integrate immunisation with anganwadi and school health visits; strengthen AEFI (adverse events following immunisation) surveillance to keep trust.
Memory Tricks
Don’t Confuse
| This | vs | That |
|---|---|---|
| Innate immunity: from birth, non-specific, no memory | vs | Adaptive immunity: acquired, specific, memory |
| B cells: antibodies (humoral) | vs | T cells: cell-mediated; mature in the thymus |
| IgG: crosses the placenta | vs | IgA: in colostrum |
| Vaccine: active immunity, memory | vs | Antiserum / anti-venom: passive, immediate, no memory |
| OPV: live, oral (Sabin) | vs | IPV: inactivated, injected (Salk) |
| Covaxin: inactivated | vs | Covishield: viral vector |
| Toxoid (tetanus): inactivated toxin | vs | Antitoxin (anti-tetanus serum): ready-made antibodies |
Common Mistakes
- “Anti-snake venom gives active immunity.” False. It gives passive immunity (ready-made antibodies).
- “IgA crosses the placenta.” False. IgG crosses the placenta; IgA is in colostrum.
- “Vaccines work by killing germs directly.” False. They train the immune system and create memory cells.
- “Covaxin is an mRNA vaccine.” False. It is an inactivated whole-virus vaccine. ZyCoV-D is a DNA vaccine.
- “The 2026 HPV campaign gives two doses to girls aged 9–14.” False. It gives a single dose to girls aged 14.
- “Hepatitis B vaccine is a live vaccine.” False. It is a recombinant subunit vaccine.
Practice
All questions below are original practice questions written in CGPSC style. They are not previous-year questions.
Level 1: Foundation
- The only class of antibody that can cross the placenta is ______.
- Edward Jenner’s smallpox vaccine (1796) used material from ______.
- The pentavalent vaccine protects against which five diseases?
Answers
- IgG.
- Cowpox.
- Diphtheria, pertussis, tetanus, hepatitis B and Hib infections.
Level 2: Prelims MCQs
Q1. Consider the following statements:
- Immunity acquired by a baby through its mother’s milk is natural passive immunity.
- Vaccination produces artificial active immunity.
- Passive immunity generates memory cells that give lifelong protection.
Which of the statements given above is/are correct?
- (a) 1 only
- (b) 1 and 2 only
- (c) 2 and 3 only
- (d) 1, 2 and 3
Answer and explanation
Q2. Match List I (Vaccine) with List II (Type):
| List I | List II |
|---|---|
| A. BCG | 1. Toxoid |
| B. Tetanus vaccine | 2. Recombinant subunit |
| C. Hepatitis B vaccine | 3. Live attenuated |
| D. Covishield | 4. Viral vector |
- (a) A-3, B-2, C-1, D-4
- (b) A-3, B-1, C-2, D-4
- (c) A-1, B-3, C-2, D-4
- (d) A-3, B-1, C-4, D-2
Answer and explanation
Q3. In which year was the Universal Immunization Programme launched in India?
- (a) 1978
- (b) 1985
- (c) 1995
- (d) 2014
Answer and explanation
Q4. The nationwide HPV vaccination campaign launched in India in February 2026 provides:
- (a) two doses of Cervavac to girls aged 9–14
- (b) a single dose of Gardasil-4 to girls aged 14
- (c) three doses to all women aged 15–45
- (d) a single dose to boys and girls aged 12
Answer and explanation
Q5. Which antibody class is chiefly involved in allergic reactions?
- (a) IgG
- (b) IgA
- (c) IgM
- (d) IgE
Answer and explanation
Level 3: Mains Answer Writing
Q1. (60 words) What is herd immunity? Why does it matter for people who cannot be vaccinated?
Model answer outline
- Definition: indirect protection of a community when a high enough share is immune, so a pathogen cannot keep spreading.
- Threshold: depends on how infectious the disease is; about 95% for measles.
- Importance: protects newborns, the very ill and the immunocompromised who cannot take some vaccines; falling coverage leads to outbreaks.
Q2. (150–200 words) Explain how vaccines provide immunity. Evaluate India’s Universal Immunization Programme, with reference to its reach in remote areas such as southern Chhattisgarh.
Model answer outline
- Intro: Vaccines expose the immune system to a harmless antigen, producing antibodies and memory B and T cells; a later infection meets a fast secondary response.
- UIP achievements:
- Launched 1985; free vaccines against 12 diseases (9 nationally, 3 sub-nationally); HPV for 14-year-old girls added in 2026.
- Polio-free certification (2014), maternal and neonatal tetanus elimination (2015).
- Mission Indradhanush (2014) catch-up rounds; eVIN cold-chain tracking; U-WIN digital registry.
- Coverage rising (survey: NFHS-5 full immunisation 76.4%; administrative data near 98% by 2026, so quote the source).
- Gaps: zero-dose children; cold-chain and access problems in forested, conflict-affected Bastar; hesitancy and myths; data mismatch.
- Chhattisgarh angle: fixed-day sessions at anganwadis, mitanins tracking due lists, outreach through haat-bazaar clinics.
- Conclusion: Closing the last-mile gap needs community trust, digital tracking and integration with nutrition and primary care.
Quick Revision Table
| Fact | Detail |
|---|---|
| Innate vs adaptive | From birth, non-specific vs acquired, specific, memory |
| B cells / T cells | Antibodies (humoral) / cell-mediated; T cells mature in thymus |
| IgG / IgA / IgM / IgE | Placenta, most abundant / colostrum / first / allergy |
| Natural passive | Placenta (IgG), colostrum (IgA) |
| Artificial passive | Anti-venom, antiserum, immunoglobulin |
| HIV | Destroys helper T (CD4) cells |
| Jenner / Pasteur | 1796 cowpox / rabies vaccine 1885 |
| Live vaccines | BCG, OPV, MR, rotavirus, chickenpox |
| Toxoids | Tetanus, diphtheria |
| ZyCoV-D | World’s first DNA vaccine for humans (India, 2021) |
| Cold chain | +2 °C to +8 °C; VVM; eVIN (2015) |
| UIP | 1985; 12 diseases (9 national + 3 sub-national) |
| Pulse Polio / Vaccination Day | 1995 / 16 March |
| Mission Indradhanush | 25 December 2014 |
| Pentavalent | DPT + Hep B + Hib |
| HPV campaign | 28 Feb 2026, Ajmer; single dose Gardasil-4; girls aged 14 |
| COVID-19 drive | Began 16 January 2021 |
Key Takeaways
- Innate immunity is the first line; adaptive immunity (B and T cells) is specific and has memory, which vaccines exploit.
- Active immunity is made by the body (infection, vaccine); passive immunity is borrowed (placenta, colostrum, anti-venom).
- Know the vaccine types with examples: live (BCG, OPV, MR), inactivated (IPV, Covaxin), toxoid (tetanus), recombinant (Hep B, HPV), vector (Covishield), DNA (ZyCoV-D).
- UIP (1985) covers 12 diseases; Mission Indradhanush (2014) targets the unreached; HPV joined in February 2026.
- Quote coverage figures with their source and date; survey and administrative numbers differ.
What’s Next
- Life Science and Human Health — Quick Revision — the whole chapter on one page
- Biotechnology — recombinant DNA, monoclonal antibodies and vaccine technology
- Welfare and Development Programmes — health and child-welfare schemes for GS-V
- Education and Human Resource Development — health as part of human development