February 29, 2008

ProQuad Vaccine Linked to Fever and Convulsions

The results of a new study presented Wednesday at a meeting of the Advisory Committee on Immunization Practices said children suffer higher rates of fever-induced convulsions after receiving the Merck combination vaccine ProQuad instead of two separate shots.

As a result, a federal advisory panel is moving away from their preference for the ProQuad, which protects against chickenpox, mumps, measles and rubella. ProQuad costs $124 per dose, about the same as the two other shots combined.

The study found children ages 12 through 23 months had seizure rates twice as high compared with those who received one shot for chicken pox and one for the other three illnesses.

The risk is equivalent to about one extra convulsion for every 2,000 doses of ProQuad, said Dr. Nicola Klein, who led the study, in an Associated Press Report. Her study was funded by the U.S. Centers for Disease Control and Prevention.

The study concentrated on children who develop fevers and subsequent convulsions, something that usually has no lingering consequences. The researchers said there were no deaths in the study.

ProQuad was licensed in 2005, but has been in short supply after Merck suspended production due to manufacturing issues.   However, the company is planning to resume production later this year.

The advisory committee had previously recommended doctors give children as few a number of shots as possible, and for that reason preferred the ProQuad vaccine.

However, on Wednesday it amended the recommendation, saying the council no longer preferred ProQuad to the separate shots.

"Safety, shortages, delivery issues - lots of reasons not to state such a strong preference," said member panel Patsy Stinchfield, an infectious disease expert at Children's Hospitals and Clinics of Minnesota, in an Associated Press report.

Representatives from Merck said their own internal research confirmed the results of the new study, and also showed a doubling of the risk in children within five to 12 days of vaccination. However, the company noted the occurrence were low, with about 5 cases in 10,000.

They said that there is five times more chickenpox antigen in the ProQuad shot than in the stand-alone shots, but said it wasn't clear that would explain the difference in the observed rates of seizures. For some reason, the difference disappears when comparing rates for 30 days, they added.

Klein's research checked seizure rates only at seven to 10 days after vaccination, and examined approximately 43,000 kids who got ProQuad and 315,000 who got the two other shots together. It found fever-related seizures occurred at a rate of 9 per 10,000 in children who received ProQuad, compared with 4 per 10,000 for those who got separate shots.


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