Exam Focus

Exam Focus

Vaccination and herd immunity are core examination topics across all boards. Edexcel 1BI0 Paper 1 (Topic 5: Health, Disease and Medicine) tests this frequently, often with stimulus-based questions presenting vaccination coverage data or graphs of disease incidence — expect to interpret data AND explain mechanisms. The topic combines biology with data interpretation and ethical discussion. Edexcel 6-mark responses on this topic require reference to the stimulus material provided as well as your own biological knowledge.

• How vaccines work (4-5 marks): Vaccine introduces antigens → activates B cells → clonal expansion → plasma cells produce antibodies → memory B cells formed → rapid secondary response on real exposure. Must include "memory cells" to earn full marks.
• Herd immunity explanation (3-4 marks): When a high proportion of the population is immune, even unvaccinated individuals are protected because the pathogen cannot spread efficiently. Explain who benefits from herd immunity (babies, immunocompromised, elderly).
• Herd immunity threshold calculation (2 marks): Know the formula Threshold = 1 - (1/R₀). Show working. Be able to use it to explain why measles needs higher coverage than flu.
• Ethical discussion (4 marks): Individual choice vs community benefit; risks of vaccine vs risks of disease; protecting vulnerable populations who cannot be vaccinated. Balance arguments — do not just list positives.

Common mark losses: Saying vaccines cause disease (they trigger immune response, not disease). Explaining herd immunity as "everyone is vaccinated" — it means enough people are immune, including naturally immune individuals. Not naming memory cells as the mechanism for long-term protection.