The live attenuated varicella vaccine that was approved in 1995 is not currently recommended by the manufacturer for postexposure prophylaxis. The older varicella vaccine preparations were shown to be effective for postexposure prophylaxis in studies done in the 1970s and 1980s. Because the vaccine manufacturing process has since changed, no studies have been performed using the currently available Oka/Merck vaccine. Salzman and Garcia evaluated the efficacy of postexposure vaccination in siblings of children with active varicella virus infection.

Each time a patient presented with the varicella virus, varicella vaccination was offered to all family members with a negative history of varicella infection. Parents were instructed to count the number of lesions on their children on the fifth day of the rash. Phone contact during the following 10 to 30 days identified the vaccinated family members who had developed lesions. Ten vaccinated siblings (14 months to 12 years of age) of seven index case patients were followed. The mean numbers of lesions were 245 in the index case patients and 13.4 in the vaccinated siblings. Five of the vaccinated siblings did not develop lesions; the five patients who did develop lesions became symptomatic 12 to 13 days after vaccination.

Previous studies have shown the attack rate of varicella among susceptible household contacts to be as high as 87 percent, considerably higher than the rate of infection in patients who received the postexposure vaccination in this study. In susceptible persons who do develop active varicella virus infection, the disease appears to be attenuated. The authors conclude that varicella vaccination should be considered in all siblings of children with active varicella virus infection who have a negative history of varicella disease or vaccination.