BharatNotes What is Vaccines and Immunity Types?
Immunity is the body's capacity to defend itself against disease-causing organisms. Immunologists divide it into two main lines of defence, and vaccines are the deliberate tool used to build one of them safely.
Types of Immunity
Innate (natural) immunity is present from birth and is non-specific — it responds the same way to all invaders. It includes physical barriers (skin, mucous membranes), chemical barriers (stomach acid), and cells such as phagocytes.
Adaptive (acquired) immunity is pathogen-specific, slower to act, and crucially generates memory cells so future encounters trigger a faster, stronger response. It operates through two mechanisms: humoral immunity (antibodies produced by B cells) and cell-mediated immunity (T cells). Adaptive immunity is further split into:
| Type | How acquired | Example | Duration |
|---|---|---|---|
| Active immunity | Body makes its own antibodies after exposure | Natural infection; vaccination | Long-lasting, sometimes lifelong |
| Passive immunity | Ready-made antibodies received | Mother to baby; antiserum injection | Short-lived |
Herd immunity occurs when enough of a population is immune (through infection or vaccination) that pathogen transmission is interrupted, indirectly protecting the unimmunised.
Types of Vaccines
A vaccine induces active immunity without causing disease. The major platforms (per WHO and the US CDC) are:
| Vaccine type | Basis | Indian examples |
|---|---|---|
| Live attenuated | Weakened live pathogen; strong, often lifelong response | BCG, OPV, Measles-Rubella |
| Inactivated/killed | Killed pathogen; needs boosters | IPV, whole-cell pertussis |
| Toxoid | Inactivated bacterial toxin | Tetanus, Diphtheria |
| Subunit/conjugate | Part of the pathogen (protein/sugar) | Hepatitis B, Hib, PCV |
| mRNA / viral-vector | Genetic instructions to make a target protein | COVID-19 vaccines (Covaxin is inactivated; Covishield is viral-vector) |
Significance and Current Status
India's Universal Immunisation Programme (UIP) is the largest in the world, annually targeting about 2.6 crore infants and 2.9 crore pregnant women through roughly 1.2 crore sessions (PIB, 2024). It provides free vaccines against 12 vaccine-preventable diseases — nationally against 9 (diphtheria, pertussis, tetanus, polio, measles, rubella, severe childhood TB, hepatitis B, and Hib-caused pneumonia/meningitis) and sub-nationally against 3 (rotavirus diarrhoea, pneumococcal pneumonia, Japanese encephalitis) — as per the National Health Mission. Full immunisation coverage stood at 93.23% for FY 2023-24 (PIB). Mission Indradhanush, launched in December 2014, accelerates coverage in low-uptake and hard-to-reach areas.
UPSC Angle
For Prelims, master the active/passive distinction, the vaccine-platform classification, and which scheme covers which disease. For Mains (GS2/GS3), link immunisation to public-health governance, the cold chain, vaccine self-sufficiency, and biotechnology. This is a foundational concept — it underpins recurring questions on immunisation drives, biotech, and health policy rather than any single past question.
