American Board of Internal Medicine (ABIM) Certification Practice Exam

What timeframe is critical for administering varicella vaccine to prevent infection?

1. Before exposure

2. 3 to 5 days after exposure

3. 5 to 7 days after exposure

4. Within 1 day of diagnosis

The correct answer is: 3 to 5 days after exposure

The critical timeframe for administering the varicella vaccine to prevent infection is 3 to 5 days after exposure. This is based on the vaccine's ability to provide immune protection when given shortly after a person has been exposed to the varicella zoster virus, which causes chickenpox. Administering the vaccine within this specific window can help to significantly reduce the severity of the disease or potentially prevent the outbreak altogether. If a person is exposed to varicella, they are at risk for developing the disease, and the post-exposure vaccination can serve as a form of prophylaxis. While vaccination before exposure is ideal for preventing the infection, post-exposure vaccination within the 3 to 5-day window is a recognized strategy to mitigate the effects of the virus. Timing is crucial; administering the vaccine beyond this timeframe—such as more than 5 days after exposure—may not provide protective effects. In contrast, other suggested timeframes for vaccination, such as within 1 day of diagnosis or after 3 days, are not effective strategies for preventing the infection post-exposure.