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For people who haven't had chickenpox and are exposed to an ill family member, getting vaccinated within five days can reduce the risk of developing chickenpox—or at least reduce the severity of disease, reports a study in the January issue of the Pediatric Infectious Disease Journal.
"Available varicella vaccines administered within five days after exposure to chickenpox are effective in preventing chickenpox and highly effective in attenuating the disease," concludes the study by Dr. Maria Brotons and colleagues of Hospital Universitario Vall d'Hebron, Barcelona.
The researchers analyzed their experience with "post-exposure prophylaxis"—giving chickenpox (varicella) vaccine after exposure to the disease—in 67 patients. The patients, including 21 children, were exposed to a family member with chickenpox. All patients received commercially available chickenpox vaccine within five days after exposure, most within three days.
Because they had not had chickenpox or received the chickenpox vaccine, the patients were at high risk of developing chickenpox. Their lack of immunity was confirmed by serologic studies. Based on past studies, it was estimated that 58 of the 67 patients would get sick after being exposed to chickenpox. However, only 22 patients developed disease after being vaccinated. Thus vaccination after exposure was about 62 percent effective in preventing chickenpox.
When chickenpox did develop, it was mild to moderate in all cases. Vaccination was estimated to be 79 percent effective in preventing moderate to severe chickenpox. There was no difference in effectiveness between children and adults, or between patients vaccinated at different times after exposure up to 5 days post-exposure.
Although it is usually a mild disease, chickenpox can have significant complications. Previous studies have suggested that vaccination after exposure can reduce the risk of developing chickenpox. The new study provides important new information on the effectiveness of currently available varicella vaccines for post-exposure prophylaxis.
The results suggest that, for people exposed to a family member with chickenpox, it's not too late to get vaccinated. Vaccination within five days reduces the risk of getting chickenpox by about 60 percent, and reduces the chances of developing moderate to severe chickenpox by nearly 80 percent. Post-exposure prophylaxis may be especially important in children and adolescents, who are at higher risk of developing rare but serious complications from chickenpox.