Clinical Question

Should varicella vaccine be given as postexposure prophylaxis for prevention in healthy unvaccinated children and adults?

Evidence-Based Answer

Varicella vaccine appears to be effective in preventing or modifying the severity of the disease in healthy unvaccinated children if administered within three days of exposure. Data are insufficient to support or refute the use of the vaccine as postexposure prophylaxis in adults and adolescents.

Practice Pointers

The probability is greater than 90 percent that varicella infection will occur in a susceptible person following exposure.¹ Secondary bacterial infection of soft tissues is the most common complication, but more serious illnesses have been reported, including pneumonia, dehydration, hepatitis, ataxia, and encephalitis.²

In this Cochrane review, the authors could not perform a meta-analysis because the included studies varied greatly in methodology and measured outcomes. However, the authors found three randomized and quasirandomized controlled trials of postexposure prophylaxis with varicella vaccine in children. In these studies, 13 of 56 vaccine recipients developed varicella, compared with 42 of 54 recipients of placebo or no vaccine (18 versus 78 percent; number needed to treat = 2). Twelve of the 13 recipients who developed chicken pox had mild disease with fewer than 50 lesions. Most participants (i.e., 70 percent) received the vaccine within three days of exposure. Therefore, it is not possible to assess the effectiveness of the vaccine in preventing or modifying the disease if given after three days of exposure because of the small number of participants who received the vaccine on days 4 or 5. There are no data regarding the potential benefit of administering a second dose to one-dose vaccine recipients after exposure. However, the Advisory Committee on Immunization Practices (ACIP) recommends giving a second dose to patients who have previously received one dose of vaccine.³

The safety of varicella vaccine when used as post-exposure prophylaxis was not adequately assessed in these three studies. Postlicensure studies of vaccine effectiveness have indicated that varicella vaccine has a good safety profile.^4,5 The most common adverse events are rash within 42 days of vaccination, fever, and injection-site reactions.³

This review does not find sufficient data to support or refute the use of varicella vaccine as postexposure prophylaxis in adolescents and adults. Nevertheless, according to ACIP, postexposure vaccination should be offered to adults without evidence of immunity. ACIP also recommends postexposure prophylaxis for all exposed household contacts.³