A virus has a basic reproduction number (R0) estimated at 5.0. Using the herd immunity threshold formula, what minimum fraction of the population must be immune to interrupt sustained transmission, and what implication does that have for an eradication campaign?

• A. About 50% of the population; this moderate target can be achieved without focusing on high-risk subgroups or boosting schedules
• B. About 80% of the population; campaigns must reach high coverage levels and account for less-than-perfect vaccine efficacy to interrupt transmission
• C. 100% of the population; eradication requires literally every individual to be immune because R0-based formulas are unreliable
• D. About 20% of the population; a relatively small fraction needs immunity so localized vaccination efforts are usually sufficient for eradication

Answer: (B)