Paper I
Question
Classify types of vaccines with one example each. Discuss advantages and disadvantages of different types of vaccines. (2+4)
Answer
Classification of vaccines with one example each:
- Live attenuated vaccine — e.g., BCG vaccine.
- Killed/inactivated vaccine — e.g., Inactivated Polio Vaccine (IPV).
- Toxoid vaccine — e.g., Tetanus toxoid.
- Subunit/recombinant vaccine — e.g., Hepatitis B vaccine (recombinant HBsAg).
- Conjugate vaccine — e.g., Haemophilus influenzae type b (Hib) conjugate vaccine.
- Polysaccharide vaccine — e.g., Pneumococcal polysaccharide vaccine (PPSV23).
Advantages and disadvantages:
- Live attenuated vaccines — Advantages: closely mimic natural infection, inducing strong, durable humoral and cell-mediated immunity, often with a single dose; can induce mucosal immunity (e.g., OPV). Disadvantages: risk (rare) of reversion to virulence; contraindicated in pregnancy and immunosuppression; requires strict cold-chain maintenance.
- Killed/inactivated vaccines — Advantages: no risk of causing the disease (no live organism); safe in immunocompromised/pregnant individuals; stable, easier storage. Disadvantages: generally weaker immune response, often requiring multiple doses and booster shots; primarily induces humoral immunity, weaker cell-mediated response.
- Toxoid vaccines — Advantages: highly effective at preventing toxin-mediated disease (e.g., diphtheria, tetanus), safe. Disadvantages: protects only against the toxin, not organism colonization, so does not prevent carriage/transmission; requires booster doses.
- Subunit/recombinant vaccines — Advantages: very safe (contains only a specific antigen, no live/whole organism); can be mass-produced consistently. Disadvantages: often less immunogenic alone, requiring adjuvants and multiple doses; production can be technically complex.
- Conjugate vaccines — Advantages: converts a poorly immunogenic T-independent polysaccharide response into a strong, memory-generating T-dependent response, effective even in infants. Disadvantages: more complex/costly to manufacture than plain polysaccharide vaccines.
- Polysaccharide vaccines — Advantages: can cover multiple serotypes. Disadvantages: poorly immunogenic in children under 2 years (T-independent response, no memory generation), limiting their use in the youngest, highest-risk age group.