Exam Tips: Vaccination and Herd Immunity

Always mention memory cells: Any question about why vaccines give long-term protection, or why a second exposure does not cause disease, must mention memory B cells. These are the key. The answer is NOT "the body still has antibodies" — antibody levels fall within weeks. It is memory cells that provide durable protection.

Herd immunity — name who is protected: When explaining herd immunity, give specific examples of who benefits: infants too young to be vaccinated, people who are immunocompromised (e.g., cancer patients on chemotherapy), elderly people with weaker immune systems, and the small proportion of vaccinated people in whom the vaccine did not generate full immunity.

Ethical questions — balance is essential: AQA requires balanced evaluation. State the benefits of vaccination (prevents disease, herd immunity, cost savings) AND the drawbacks (rare side effects, individual choice, religious objections). Then conclude with which side you think has stronger evidence. Do not just list advantages.

Herd immunity threshold calculation: Show all working: write the formula, substitute R₀, calculate the answer, convert to a percentage. Even if you get the final answer wrong, showing the correct method earns working marks. Practice with different R₀ values.

Link vaccination to secondary response explicitly: On first vaccine dose: primary response, memory cells formed. On booster dose (or real infection): secondary response — faster, higher antibody levels, no symptoms. This explicit linkage between vaccine mechanism and secondary immune response is what separates 5-mark answers from 3-mark ones.