CDC reports more seizures seen in toddlers given combined shot; experts stress real risk is still low
THURSDAY, March 13 (HealthDay News) -- U.S. health officials are no longer recommending the combination MMRV (measles, mumps, rubella and varicella) vaccine over the MMR vaccine and a separate varicella vaccine for kids.
The change comes after new data show that the MMRV shot increases the risk for febrile seizure in children aged 12 to 23 months. Preliminary findings suggest there is a doubling in the relative increased risk in this age group within a week to 10 days after receiving the shot, according to a report in the March 14 issue of the Morbidity and Mortality Weekly Report, published by the U.S. Centers for Disease Control and Prevention.
Based on the preliminary data, the CDC'S Advisory Committee on Immunization Practices (ACIP) is withdrawing its preference, issued last year, for the combination vaccine over the two separate injections.
But the absolute risk of febrile seizures is still low, experts stressed.
"The relative risk doesn't really give parents the true understanding of what's happening," said Dr. Robert Frenck, a professor of pediatrics at Cincinnati Children's Hospital. "A big pediatric practice maybe has 100 newborns a month added to its practice, so that they may see one [incidence of febrile seizure related to the vaccination] a year."
And because of manufacturing difficulties, the MMRV shot, made by Merck, won't really be available until about this time next year, added Frenck, who is a member of the American Academy of Pediatrics' committee on infectious diseases.
The MMRV was licensed by the U.S. Food and Drug Administration on Sept. 6, 2005, for use in children aged 12 months to 12 years. The first dose was recommended at 12 to 15 months, and the second at 4 to 6 years.
But the Vaccine Safety Datalink (VSD), which monitors vaccine safety, detected a signal for increased seizures in children aged 12 to 23 months who got the MMRV shot compared with those who got the MMR one (many children also got varicella). The MMR shot is also known to cause febrile seizures, Frenck said.
The VSD then initiated a study of 43,353 children aged 12 to 23 months who received the MMRV vaccine and 314,599 children aged 12 to 23 months who received the MMR vaccine and varicella vaccine during the same visit, according to the CDC report.
"The preliminary results indicated a rate of febrile seizure of nine per 10,000 vaccinations among MMRV vaccine recipients compared with four per 10,000 vaccinations among MMR vaccine and varicella vaccine recipients," the CDC reported. "These results suggest that, in the 7-10 day post-vaccination period, approximately one additional febrile seizure would occur among every 2,000 children vaccinated with MMRV vaccine, compared with children vaccinated with MMR vaccine and varicella vaccine administered at the same visit."
On Feb. 27, the ACIP was informed about the heightened risk.
Febrile seizures are convulsions brought on by fever, usually from common childhood illnesses such as middle ear infections, viral upper respiratory tract infections and roseola. Although the seizures are distressing, children generally recover, according to the CDC.
"Practically speaking, it means little," said Dr. Paul A. Offit, director of the Vaccine Education Center and chief of infectious diseases at the Children's Hospital of Philadelphia. "The attributable risk of fever is still quite low. I think the committee thought the better part of valor was at least not to express a preference for one over the other. For the most part, MMRV is not particularly available, so there's little or no impact."
There is no data yet on the risk for febrile seizures after the second MMRV vaccine, which is given at 4 to 6 years of age, although previous research showed that the second dose is less likely to cause fever than the first.
The changes have nothing to do with a possible vaccination link to autism, Frenck said.
The Vaccine Safety Datalink has more on vaccine and febrile seizures.
SOURCES: Robert Frenck, M.D., professor, pediatrics, Cincinnati Children's Hospital, and member, American Academy of Pediatrics committee on infectious diseases; Paul A. Offit, M.D., director, Vaccine Education Center, and chief, infectious diseases, Children's Hospital of Philadelphia; March 14, 2008, Morbidity and Mortality Weekly Report, U.S. Centers for Disease Control and Prevention
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