CDC clarifies preference on childhood vaccines

WASHINGTON (Reuters) - Children who get a combined vaccine against measles, mumps, rubella and chicken pox are slightly more likely to have seizures compared to those getting two separate shots for the same diseases, U.S. officials said on Thursday.

The seizures are not usually life-threatening and the U.S. Centers for Disease Control and Prevention said it was no longer expressing a preference that children get the so-called MMRV combined vaccine rather than two shots -- the MMR vaccine against measles, mumps and rubella (German measles) and a separate one against varicella (chicken pox).

The CDC said it made the change after seeing evidence that children who got the combined MMRV vaccine faced an elevated, but still very small, risk of suffering febrile seizures after vaccination compared to those who got the two shots.

A febrile seizure is a convulsion in young children associated with an increase in body temperature, often from an infection. While frightening, the seizures are not usually dangerous and only a small percentage of children who experience one go on to develop epilepsy.

Dr. John Iskander, the acting director of the CDC's Immunization Safety Office, said it remained very important that parents get their children vaccinated against these diseases.

"These are vaccines that have had enormous public health benefits," Iskander said.

The CDC said the availability of the MMRV vaccine, made by pharmaceutical company Merck, already was limited in the United States because of manufacturing constraints unrelated to vaccine safety, and was not expected to be widely available until 2009.

The CDC said a study examined the risk for febrile seizures seven to 10 days after vaccination among 43,353 children ages 12 months to 23 months who received the MMRV vaccine and 314,599 children of the same age who received the MMR vaccine and chicken pox vaccine administered separately.

It found a rate of febrile seizure of nine per 10,000 vaccinations among MMRV recipients, and four per 10,000 among children who got separate MMR and chicken pox shots. Of 166 children who had febrile seizures after either type of vaccination, 26 were hospitalized and none died, the CDC said.

(Reporting by Will Dunham; Editing by Maggie Fox and Eric Beech)