A novel virus has R0 = 5.0. A vaccine with 80% efficacy is available. What minimum proportion of the population must be vaccinated to prevent sustained transmission? Show your calculation.

• A. 62.5% coverage is sufficient because you should multiply the HIT by the vaccine efficacy (0.8 × 0.8 = 0.64) and round down to reflect real-world constraints, so roughly 62.5% is acceptable.
• B. 100% vaccination coverage is required because the adjusted coverage = HIT/VE = 0.8/0.8 = 1.0, meaning everyone must be vaccinated with an 80% effective vaccine to prevent sustained spread.
• C. No vaccination strategy can achieve herd immunity for R0 = 5.0, therefore the only option is to rely on natural infection to reach population immunity faster than any vaccination campaign.
• D. 80% vaccination coverage is enough because the herd immunity threshold is 80% for R0 = 5.0 and vaccine effectiveness does not alter required coverage estimates in practice.

Answer: (B)