Unimmunized Kids Less Likely to Get Chickenpox if Vaccinated After Exposure

“Better late than never” might be a true statement when it comes to vaccinating children for chickenpox, according to a new review of studies. Only 18 percent of children given the vaccine within the 3 days following exposure to chickenpox developed the infection, compared with 78 percent of children who had received an inactive placebo or no vaccine.

The review was intended to “look at the use of the currently licensed chickenpox vaccine in preventing chickenpox in a person who has been exposed to the disease, but has no history of being immune through vaccination or previously having the disease,” said Kristine Macartney, MD, a pediatrician at the National Centre for Immunisation Research in Sydney, Australia.

In most healthy children, chickenpox infection involves only a rash, fever and other uncomfortable symptoms, but 1 percent of kids infected with chickenpox develop potentially serious complications, such as bacterial infection, pneumonia, dehydration, hepatitis and encephalitis.

The varicella zoster virus can also remain dormant in the body after infection, and then later in life flare into a blistering, painful rash commonly known as shingles.

The authors, led by Macartney, looked at three studies that included 110 healthy children, all of whom were exposed to chickenpox when a sibling developed the infection. The studies spanned a 27-year period and took place in Japan, the United States and Israel.

The review appears in the latest issue of The Cochrane Library, a publication of The Cochrane Collaboration, an international organization that evaluates medical research. Systematic reviews draw evidence-based conclusions about medical practice after considering both the content and quality of existing medical trials on a topic.

In the studies, not only did fewer vaccinated children develop chickenpox, but those who did only had a mild form of the disease, with less than 50 skin lesions. None of the studies evaluated the effects of postexposure varicella vaccination in adolescents or adults.

“These studies seem to suggest that these vaccines will be effective within three days of exposure to chickenpox, and even if mild chickenpox occurs, the vaccine is likely to prevent moderate to severe cases,” Macartney said.

However, the studies did not provide much information on a longer timeframe, so the authors could not say whether giving the vaccine four to five days after exposure would be effective, Macartney said.

Although she called the review “very well done,” U.S. expert Jane Seward was unsurprised by the reviewers’ findings. Seward is the deputy director of the Division of Viral Diseases, National Center for Immunizations and Respiratory Diseases, at the Centers for Disease Control and Prevention (CDC).

“We’ve had a recommendation of postexposure use for nearly a decade,” said Seward, who had no affiliation with the review.

In 1999, the CDC’s Advisory Committee on Immunization Practices first recommended the use of the varicella vaccine as a method of controlling chickenpox outbreaks and preventing illness in children and adults who do not have immunity but who have been exposed to the virus.

The current review did not assess side effects of the vaccine, such as injection reactions and fever, although Macartney said that other studies have shown few adverse events to be associated with the vaccine. “There’s not really a reason to suspect it would be different,” she said.

In general, the authors say in the review that the lack of available study data is a limiting factor for research on the effectiveness of postexposure varicella vaccination.

“Despite the varicella vaccination having been around for a long time, it’s not been examined in this context in a number of well-designed studies,” Macartney said.

Although they are not included in the current review’s results, observational and unpublished studies with similar postexposure findings support the authors’ conclusions, Seward said.

The American Academy of Pediatrics (AAP) recommends that children receive one dose of varicella vaccination between 12 and 18 months of age. People who do not receive the vaccine until 13 years of age should receive two doses of varicella, four to eight weeks apart, the AAP suggests.

Public health officials in the United States, Canada and Australia recommend routine universal varicella vaccination, so the review results are probably less relevant than in other countries where the chickenpox vaccine is available, but not routine, Macartney said.

“Hopefully this review provides some weight to postexposure prophylaxis that healthcare practitioners may want to consider,” she said.

Reference: Macartney K, McIntyre P. Vaccines for post-exposure prophylaxis against varicella (chickenpox) in children and adults (Review). Cochrane Database of Systematic Reviews 2008, Issue 3.

Source: The Cochrane Collaboration

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