Children whose parents refuse to let them be vaccinated for chickenpox are nine times as likely as vaccinated children to develop chickenpox that requires medical attention, researchers reported Monday.
Although the conclusion may seem self-evident, it reflects a growing problem with childhood immunizations, said epidemiologist Jason M. Glanz of Kaiser Permanente's Institute for Health Research in Denver, the lead author of the report in the Annals of Internal Medicine. Immunizations have been so successful, he said, that some parents are becoming more concerned about the risks of vaccines than they are about the illness.
"Vaccines are becoming victims of their own success," he said.
The vaccine for chickenpox, formally known as varicella, is one parents are most likely to skip because they believe the disease is the least serious preventable childhood illness. But before the varicella vaccine was introduced in 1995, about 4 million U.S. children contracted chickenpox every year, with 10,000 hospitalizations and 100 deaths. Those figures have subsequently been reduced by more than 80 percent.
Chickenpox is characterized by a high fever, an itchy rash, red spots or blisters all over the body, and malaise. It also renders children more susceptible to other infections and can leave permanent scarring.
Complications can be especially severe in children with compromised immune systems due to AIDS, certain other diseases and anti-rejection treatments after transplants. Such children frequently cannot be immunized, and the best way to prevent them from falling ill is to inoculate other children in the community, blocking the spread of the disease.
Glanz and his colleagues studied the electronic health records of 86,993 children ages 1 through 8 who were members of the managed-care group Kaiser Permanente Colorado, identifying 133 physician-confirmed cases of varicella. They then compared these children to 493 others, matched for age and gender, who were not infected.
Many of the varicella cases occurred in children too young to be vaccinated, in children who had recently been vaccinated or when it could not be confirmed whether the parents refused vaccination.
The researchers concluded, however, that seven of the cases, about 5 percent, were in children whose parents refused vaccination, and that those children were nine times more likely to contract the disease than those in the age- and gender-matched control group. One of them had a severe complication, a streptococcal infection that led to hospitalization.
Although the numbers were small, the results were statistically significant.
"The common perception among parents is that they don't believe chickenpox is a serious illness, and they don't believe their children are at risk," Glanz concluded. "This study shows that they are wrong on both counts."
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