<prompt> What is the ideal time for staing post-exposure prophylaxis with acyclovir in a person exposed to varicella?Immediately after exposure3rd day7-9 th day10-14 th day  <response>: Antiviral therapy for prophylaxis against varicella should be staed 7 days after the intense exposure, using acyclovir. Ref: Harrisons Principles of Internal Medicine, 18th edition, Page: 1466 