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Chickenpox vaccine works, but how well?
By WES ALLISON, Times Staff Writer
Julie Maguire figured the dots on her son's face and belly must be heat rash. He was too young for acne, and he had been vaccinated against chickenpox almost five years ago. She sent him to the showers. But the bumps didn't disappear, and they persisted the next morning -- tiny red welts, round and a little itchy. Maguire became suspicious as she perused the Internet for culprits, then heard one of M.J.'s classmates was home with the chickenpox. There was no doubt about it. And she couldn't have been more surprised. "Since he had the vaccine, it was the last thing on my mind," Maguire said last week from her St. Petersburg home. "And he wasn't really sick. He didn't feel bad." M.J., who is 10, and his mom discovered an emerging fact about the varicella vaccine, which is now required for all children when they enter school: It may not be as good at preventing chickenpox as was previously thought. In an article published this month in the New England Journal of Medicine, researchers revealed that during an outbreak of chickenpox at a large New Hampshire day care center, more than half the children who had been vaccinated still got the disease -- a prevention rate of just 44 percent. And the more time that had passed since they were vaccinated, the more likely the children were to get sick. Earlier studies had suggested the vaccine was 70 to 90 percent effective. The new finding has prompted federal health officials to begin studying whether a booster shot may be needed. "Figuring out the best (vaccination) schedule takes time," said Dr. Karin Galil, the article's lead author. "Once a vaccine is licensed, and millions of children and adults use it, you learn a lot more about it. There's a natural process of evolution that occurs." Galil and other experts stressed the study also confirmed the vaccine's ability to prevent severe cases of chickenpox, one of its chief benefits. Of vaccinated children who still got chickenpox at the New Hampshire day care center, 88 percent had a mild case, which was characterized by having less than 50 bumps. Among those who had not been vaccinated, only 25 percent had a mild case. Overall, the vaccinated children missed less day care, had lower fevers and didn't feel as bad as the unvaccinated children, Galil said. "That's far, far better than taking the risk of getting natural disease," said Galil, who led the investigation as a medical epidemiologist with the U.S. Centers for Disease Control and Prevention. She now works for a private drug company. Dr. Daniel Van Durme, vice chairman of the department of family medicine at the University of South Florida in Tampa, who has given thousands of varicella shots, agreed. "Your kid still has a lot of protection," he said. Although most people who get the chickenpox simply spend two weeks in misery, it can be dangerous. About 100 adults and children die from varicella each year in the United States, and most don't have some other medical condition that puts them at more risk, Galil said. Thousands more are hospitalized. "Most children are going to be very well protected, but most of all they're going to be protected from the really bad things that can happen from this virus," Galil said. Florida requires incoming prekindergarten and kindergarten students to be vaccinated or show they've had chickenpox. About half the states have similar rules, and about 75 percent of American toddlers were vaccinated last year, the CDC says. State and local health officials don't keep track of chickenpox cases, but it's most common in winter and early spring. Jan Herzik, principal at the Canterbury School of Florida in St. Petersburg, where M.J. Maguire is a student, said three children had contracted chickenpox so far this year. M.J. and one other had been vaccinated, while the third had not. These were the first chickenpox cases there in at least two years, she said. Before the vaccine became widely available in 1996, outbreaks were a yearly occurrence, and infected students usually missed two weeks. "I was saying, gosh, we're lucky, and then here we go," Herzik said. "But I tell you, the outbreak is not as severe as it's been in the past, so that's great." But because her son was probably contagious before she realized he had chickenpox, Maguire said she worries it may spread. "I think it's important for parents to be on the lookout," Maguire said. "With that vaccine, I didn't expect it at all, and I'm afraid he did infect other children because I wasn't aware." The New England Journal of Medicine study was based on an outbreak at a rural New Hampshire day care between Dec. 1, 2000, and Jan. 11, 2001. Because the school thought to call the health department, and the health department thought to call the CDC, epidemiologists were given a rare chance to study the vaccine's effectiveness in a controlled setting where children were certain to have been exposed. Past studies gauging the vaccine's effectiveness relied heavily on people who simply may have been exposed to the virus, said Galil, who has studied varicella for almost eight years. They traced the outbreak to a 4-year-old boy who had been vaccinated three years earlier. He infected 24 other children at the day care, including 16 who had been vaccinated. Children who were vaccinated more recently were the least likely to become infected. Van Durme and Dr. Juan Dumois, chairman of pediatric infectious diseases at All Children's Hospital in St. Petersburg, said the study was too small and too new to begin recommending booster shots, but it should inspire more research. Health officials had a similar experience with another, more dangerous childhood disease, the measles. After tracking occasional outbreaks in the two decades after the measles vaccine was introduced in 1963, federal health officials decided in 1989 that children should get a booster shot. That's why children today get a measles shot -- typically given with mumps and rubella shots -- as toddlers, then a booster just before starting school. "We're pushing nearly 30 years before we realized you needed a second measles shot," Van Durme said. "Because we have better surveillance, because we are aware of what happened with measles, we have a higher level of surveillance or suspicion that we might have to do the same thing with this virus." But, he added, measles is much more dangerous. "With chickenpox, if it takes a few years to figure out we need a booster, that's not a big deal."
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