Children suffered higher rates of fever-related convulsions after receiving Merck’s ProQuad combo vaccine instead of two separate shots, according to a new study. And the results prompted a federal advisory panel on vaccines to water down their preference for ProQuad, which protects against measles, mumps and rubella as well as chickenpox, the Associated Press reports.

In the study of children ages 12 months through 23 months, the seizure rate was twice as high in toddlers, compared with those who got one shot for chickenpox and one for the three other diseases. The risk translates to about one extra case of convulsion for every 2,000 doses of ProQuad, according to Nicola Klein, who lead the federally funded study and presented the data to the Advisory Committee on Immunization Practices. The study focused on children who develop fevers and then go into convulsions — an occurrence that frightens parents but usually has no lingering consequences, the AP writes, adding that there were no deaths in the new study.

ProQuad was licensed in 2005 and has in extremely short supply since last year, when Merck suspended production because of manufacturing problems. The company expects to resume ProQuad production next year. The ACIP previously decided that they preferred docs give children as few needlesticks as possible, and that ProQuad is preferable to giving separate shots. But yesterday the panel voted that it no longer has a preference.

“Safety, shortages, delivery issues — lots of reasons not to state such a strong preference,” member panel Patsy Stinchfield, an infectious disease expert at Children’s Hospitals and Clinics of Minnesota, the AP reports. Merck says its own research, though preliminary, also showed a doubling of the risk in children within five to 12 days of vaccination. However, the occurrence was low - about 5 cases in 10,000, according to the AP.

They said there was five times more chickenpox antigen, the key ingredient, in the ProQuad shot than in the stand-alone chickenpox shot. But they said it’s not clear that would explain the difference in seizure rates. For some reason, the difference disappears when comparing rates for 30 days, Merck officials maintain.

Klein’s research checked seizure rates only at seven to 10 days after vaccination, and looked at about 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 children vaccinated with ProQuad, compared with 4 per 10,000 for those who got separate shots. Klein is co-director of Kaiser Permanente Vaccine Study Center in Oakland, California, one of seven study sites. Her work was funded by the US Centers for Disease Control and Prevention.

ProQuad costs $124 per dose, about the same as the two other shots combined.

Source: The Associated Press