Chickenpox vaccine is not yet up to scratch

April 27, 2007|By Shari Roan | Shari Roan,Los Angeles Times

The chickenpox vaccine has not been a slam-dunk success. With some people, it hasn't scored any points at all.

The varicella vaccine was introduced in the United States in 1995 as a single shot given to children ages 12 months to 18 months, and by many accounts, the program has been effective.

A generation of children has been vaccinated against chickenpox, and cases of the disease have dropped by 85 percent since 1995. Deaths from severe cases of the disease fell from 124 in 1994 to 26 in 2001.

But the itchy, infectious disease is still cropping up.

A recent study in the New England Journal of Medicine found that a single shot does not produce a sufficient immune response in as many as 20 percent of people who receive it. As a result, older children, teens and young adults are developing the disease even though many have been vaccinated -- and they historically become much sicker from chickenpox than young children.

A federal government advisory committee recommended last summer adding a booster shot to the varicella vaccine regimen, and the Centers for Disease Control and Prevention is expected to publish a final recommendation this summer supporting the two-shot regimen.

"Varicella immunity has unique factors associated with it," says Dr. Roger Spingarn, a Newton Centre, Mass., pediatrician who has followed the development and use of the vaccine. "If the immunity wears off, a population of adults, now susceptible to infection, may be created."

Public health officials say a two-shot regimen would create a larger pool of fully immunized people and should reduce so-called breakthrough disease.

But health officials admit they don't yet know if a second dose would provide permanent immunity.

"The main public health concern here is that teens and young adults will get chickenpox and need to be hospitalized or will have severe illness that requires intensive care. That is the group everyone is concerned about," says Dr. Matthew Davis, an assistant professor of pediatrics at the University of Michigan who studies immunization issues.

Outbreaks are occurring regularly in "highly vaccinated" school communities, according to the study published in March in the New England Journal of Medicine.

And the disease pattern is changing. Before 1995, 73 percent of cases of varicella occurred in children age 6 or younger; now the peak incidence of the disease is 6 to 12. The study also found that the more time that elapsed since getting the shot, the more likely children were to have moderate to severe cases of the disease.

Though many breakthrough cases in vaccinated children are reported to be mild, the children are still infectious and can pass the disease to unvaccinated older people.

"The new data on waning immunity puts the recommendation of a second dose in a different light," Davis says. "It may be very important to help protect individuals for longer."

Once a person contracts the varicella virus, it never completely leaves the body, lying dormant in nerves. Sometimes, however, it is reactivated, for reasons that are not clearly understood. When this happens, the result is a painful rash -- shingles -- along the path of one or more nerves.

Although many doctors think the vaccine given in childhood will protect against shingles, public health experts aren't sure.

And adults who had chickenpox might end up more prone to shingles at a younger age because they won't get that natural immunity boost from disease that is circulating in the population, suggests Dr. James Cherry, a professor of pediatrics at Mattel Children's Hospital at the University of California, Los Angeles, and an expert on childhood vaccination.

"Our immunity is stimulated by being exposed to the chickenpox," he says. "When that stimulation goes away, our protection is going to decrease, so we'll see more cases of shingles. My guess is that we're going to be giving doses of the [varicella] vaccine to 30- and 40-year-olds to prevent shingles. The better we do [in eradicating chickenpox], the more we're going to see shingles."

Shari Roan writes for the Los Angeles Times.

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