After 14-year study, Kaiser finds chickenpox vaccine highly effective
on April 9, 2013
A rash followed by itchy, fluid-filled blisters all over a child’s body, usually tells parents their child has chickenpox. The illness was once a standard part of growing up—and many have the scars to prove it—but since a vaccination became common practice, fewer kids contract the virus. In 1995, the Advisory Committee on Immunization Practices, a group of medical and public health experts at the Center for Disease Control and Prevention (CDC) who recommend which vaccines should be used routinely in the United States, gave the thumbs up for a chickenpox vaccine.
This month, the Kaiser Permanente Vaccine Study Center, based in Oakland, released the results of a 14-year study on the vaccine’s efficacy. According to Roger Baxter, co-director of the center and an author of the study, this is the longest and largest study that Kaiser has done on the vaccine.
The results, published in this month’s issue of Pediatrics, a medical journal for the American Academy of Pediatrics, concluded that the vaccine is 90 percent effective in reducing a child’s chance of catching chickenpox. For those children in the study who did develop the virus, a second dose of the vaccine was given between 2006 and 2009. No children got a second case of the chickenpox after receiving the second dose.
“Varicella vaccine is effective at preventing chicken pox, with no waning noted over a 14-year period,” the study’s authors concluded. “One dose provided excellent protection against moderate to severe disease, and most cases occurred shortly after the cohort was vaccinated.”
“This is a very good vaccine, and it’s really effective,” said Baxter.
The study followed 7,585 children from ages 12 to 23 months who were all given the varicella vaccine in 1995 to assess its long-term effectiveness. For 14 years, researchers then called or sent note cards to their parents every six months to check to see if the child had developed chickenpox. They reminded parents what the symptoms are and what to look for. Parents were also given a phone number to report if their child developed the virus.
“We chased them down no matter where they went” to make sure researchers could keep track of the children, said Baxter.
Researchers observed that once the varicella-zoster vaccine, as it is technically called, was administered to the children, its effect did not get weaker. “Most vaccinations, we see they work for a while and then over the years they get weaker. We didn’t see that with this vaccine. It looked great over the 14 years,” said Baxter.
Still, 10 percent of the kids in the study still did contract the chickenpox after being vaccinated. “We know nothing is 100 percent in this world. We wouldn’t expect it to be 100 percent effective,” said Baxter of the vaccine. “We expected some children wouldn’t respond.”
According to Baxter, there are a variety of reasons a person could still develop a virus even after they have received a vaccination. The drug could have become less effective once injected into a person, the drug could have been left on the shelf too long, or a researcher might not have drawn the right amount of medicine, among other reasons.
The highly contagious varicella-zoster virus causes blister-like rashes, itching and fever in chickenpox. It can be serious in infants and adults with underlying health conditions or people with weakened immune systems. The airborne virus can spread easily to people who have never had the condition by touching, coughing and sneezing. The infection usually lasts for 5 to 10 days. In most cases, once a person has the chickenpox, they are immune to the disease for the rest of their life.
According to the CDC, before a vaccine existed about 4 million people would get the disease each year, about 10,600 people were hospitalized and 100 to 150 died annually because of chickenpox. But the organization also found the number of chickenpox cases had fallen by as much as 90 percent in 2005 compared to 1995.
In California, since 2001 the state has required children entering school or attending childcare to show proof of chickenpox immunization or disease history under the California Immunization law.
“All children under 18 years of age from out of state or country who enter a California school for the first time after July 1, 2001, require immunization against varicella or acceptable documentation by a health care provider’s office or clinic that the child has had the chickenpox disease,” said Gil Chavez, deputy director of the Center for Infectious Diseases at the California Department of Public Health.
“Diseases like chickenpox spread quickly, so children need to be protected before they enter school,” said Chavez.
The CDC recommends that children from the age of 12-15 months to get the vaccine dose of the vaccine and the second dose at 4 to 6 years old.
But some parents are still skeptical about the vaccine. “I have opted out of vaccines for chickenpox, as well as all other vaccines, because of my extensive research and understanding of the physiology behind naturally acquired immunity and artificial protection offered by vaccines,” said Richmond resident Kacie Flegal, who has a 21-month old son.
Despite the Kaiser study results, she does not plan to give her son the vaccine. “I am confident that if he were to acquire a case of wild chickenpox that he would have a mild case. The risk of what could occur with the vaccine is greater in my mind than him actually getting chickenpox naturally.”
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