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A growing amount of data from household, hospital, and community settings shows that administration of the varicella vaccine postexposure is effective in preventing illness or decreasing severity of infection when given within three — and possibly as many as five — days following exposure. Based on those data, the Advisory Committee on Immunization Practices now recommends use of the vaccine in susceptible individuals following exposure to the virus.
When initial exposure to the virus does not cause infection, the vaccine will provide protection from development of infection associated with future exposure. When initial exposure does lead to infection, no evidence suggests that the vaccine will worsen side effects or increase likelihood of those effects. In fact, evidence suggests just the opposite.
Transmission of the vaccine virus has been documented in only three cases of 15 million doses of vaccine. All three of the cases were mild and without complications.
[For details, see MMWR 1999; 48(RR-6).]