Under which circumstances is ring vaccination not appropriate?

• A. When transmission is widespread and vaccine supplies are limited.
• B. When transmission is focal and vaccine supplies allow targeted vaccination.
• C. When population acceptance is high.
• D. When there is no risk of exposure.

Answer: (A)

Ring vaccination works best when you can quickly identify a case and vaccinate a limited circle of contacts to create a protective buffer around it. It relies on transmission being identifiable and contained, and on having enough vaccine to reach those contacts promptly. When transmission is widespread and vaccine supplies are limited, trying to ring-vaccinate around every case would require vaccinating too many people and wouldn’t stop the spread effectively, so this approach isn’t appropriate in that situation. If transmission is focal and vaccines are sufficient for targeted vaccination, or if acceptance is high, the strategy can still be effective; and if there’s no exposure risk, ring vaccination isn’t needed.