ATLANTA, June 30 — The government’s vaccine advisory panel has endorsed giving an infant varicella vaccine either by itself or in combination with the measles-mumps-rubella vaccine (MMR).
In doing so, the Advisory Committee on Immunization Practices (ACIP) rejected the opinion of the majority of members on the working group that crafted options for the vaccination recommendations.
Most members supported separate administrations of the MMR and varicella vaccines because of a lower risk for febrile seizures in the first two weeks after receiving the shots.
The committee had originally recommended the use of the four-vaccine combination, known as ProQuad, because it reduces the number of shots and presumably increases immunization rates.
But, in March 2008, that preference was removed following preliminary data from two studies that detected an increased risk of febrile seizures with the combination.
One was a postlicensing study conducted by Merck, which makes ProQuad, and the other a study using information from the Vaccine Safety Datalink. At that time, ACIP recommended forming a working group to explore the issue. Final results of the two studies confirmed that the risk of febrile seizure doubled when using the combination vaccine for the first dose, with the risk confined to a window of five to 12 days after vaccination.
The increased risk equates to one additional febrile seizure per approximately 2,300 doses administered, according to Nicola Klein, MD, PhD, of Northern California Kaiser Permanente in Oakland.
Extrapolating that to the average practice, most pediatricians would see just one additional febrile seizure every 15 years, according to S. Michael Marcy, MD, of the University of California Los Angeles Center for Vaccine Research in Torrance, an ACIP member.
“That seems to me a fairly small price to pay when you look at the probable increase in compliance,” he said.
He and other committee members expressed concern that a stated preference for separate MMR and varicella vaccines would cause vaccine coverage and, thus, disease prevention to suffer.
But other committee members, including Lance Chilton, MD, of the University of New Mexico in Albuquerque and a practicing pediatrician, said the psychological toll of febrile seizures should be taken into account, even though the seizures have an excellent prognosis.
As one pediatrician put it in a survey of perceptions of febrile seizures, “The kids are fine and it takes the parents years to recover.”
Dr. Chilton said, “While I recognize [Dr. Marcy's] point about the fact that this doesn’t add very much to my febrile seizure quotient, I would want to avoid any febrile seizures I could.”
Proponents of a preference for the separate MMR and varicella vaccines had concerns about needing to stock the MMR vaccine, the varicella vaccine, and the combination vaccine.
Committee member Mark Sawyer, MD, of the University of California San Diego and Rady Children’s Hospital San Diego, was hesitant to provide a recommendation for separate vaccines because it would effectively, if not explicitly, eliminate the combination option.
He said clinicians would be unlikely to choose the combination in such a scenario because of perceived liability issues.
Ultimately, the committee decided that the benefits of the combination vaccine outweighed the risks and voted 10 to four to leave a preferred vaccine choice out of the recommendations.
Final data from the two studies presented to the committee did not show evidence of an increased risk for febrile seizure for 4- to 6-year-olds who received their second dose from the combination vaccine.
For this reason, ACIP agreed to defer guidance for the second dose to general language favoring combination vaccines over separate injections of their component vaccines.
Dr. Klein reported receiving research support from Merck.
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