Vaccine for Chickenpox

by Food and Drug Administration (FDA)

The days when nearly everyone spent a week of their childhood with the itchy, miserable rash of chickenpox may be on the wane. Last March 17, the Food and Drug Administration licensed a new vaccine, Varivax (varicella virus vaccine live). Commonly known as the chickenpox vaccine, it will prevent the typical cases of itchy, uncomfortable, week-long rashes and mild fevers, and the rarer cases of serious illness caused by the virus.

Although chickenpox is generally mild and not normally life-threatening, the Centers for Disease Control and Prevention estimates that there are 9,300 chickenpox-related hospitalizations and 50 to 100 deaths annually, mainly among young children.

Before receiving approval from FDA, researchers tested Varivax in about 11,000 children and adults. Scientists predict that it will be 70 to 90 percent effective in preventing the disease. Of those who did get chickenpox after vaccination, almost all had a mild form of the disease.

Adverse reactions to the vaccine were generally mild and included pain, rash, hardness, and swelling at the injection site, fever, and generalized rashes.

Mary L. Kumar, M.D., chief of pediatric infectious diseases at MetroHealth Clinic in Cleveland, tested the vaccine on about 500 children and 200 adults in the Cleveland area. She says the vaccine trials were very easy to recruit for. "We actually had people calling us," Kumar explains, adding that there was not only great interest from parents who wanted to spare their children from the disease, but also from adults in health-care professions who were concerned about getting chickenpox themselves and about infecting susceptible patients.

Will It Last?

Throughout the development of the chickenpox vaccine, there has been concern about whether the vaccine would confer lifetime immunity or simply delay infection until adulthood. When adults get chickenpox, the cases are usually more severe and the risk of complications such as pneumonia greater.

"Over the period of time it's been looked at carefully, which is about five years, we're not able to find evidence for substantial waning in immunity," says Philip Krause, M.D., senior research investigator in FDA's Center for Biologics Evaluation and Research. "It's complicated to determine how long immunity lasts, because right now people who are vaccinated are exposed to children who have [naturally acquired] chickenpox and they presumably are getting a booster effect from those repeated exposures."

"Longer is more difficult to tell," says Krause. "The only way to sort that out is going to be to see what happens after the vaccine is introduced." At FDA's request, Merck will follow several thousand vaccinated children for 15 years to determine the long-term effects of the vaccine and possible need for a booster immunization.

Shingles

As with the question of immunity, more time is needed to answer another question about the vaccine--will it cause shingles in adulthood?

Shingles is the second act of chickenpox. Once someone has had chickenpox, the virus doesn't die, it simply becomes dormant. It lingers in the body's nerve cells next to the spinal cord. Then, for reasons still not definitely known but possibly related to a weakened immune system, the virus reactivates and infects nerve fibers, causing severe pain, burning or itching. Because weakened immunity often accompanies aging, shingles usually occurs after age 50.

Can the chickenpox vaccine, which is a weakened form of the live virus, cause shingles?

"Nobody's sure what the effect will be," says Krause. "We really don't have the data to say what's going to happen in 20 to 30 years. Based on our knowledge of how the virus works and the data available so far, it doesn't appear that the rate of shingles cases in vaccinated individuals will be any greater than in the naturally infected population. There's some data in children who were immunocompromised that suggests that the vaccine may reduce the likelihood of shingles over the short term. But more data are required to determine the effect of the vaccine on shingles in healthy individuals over a lifetime."

Just One or Two Shots

A single injection of the vaccine is recommended for children ages 12 months to 12 years, while two injections four to eight weeks apart are recommended for adolescents and adults who have never had chickenpox.

"We're not really sure why teens and adults don't get immunity with one shot," says Krause. "The immune response to a single shot if you're 13 or older is not nearly as good as it is if you're younger. But two shots provide immune responses comparable to what younger people get."

For children, the vaccine has been shown to be safe and effective and can be administered at the same time as the measles, mumps and rubella vaccine. (The MMR vaccine is given at 15 months and again between 4 and 6 years or before junior high or middle school. See "Kids' Vaccinations Get a Little Easier," in the March 1994 FDA Consumer.) Public health officials hope that being able to give the chickenpox vaccine along with an already scheduled vaccine will encourage vaccination.

About the Author

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