The Centers for Disease Control and Prevention's Advisory Committee on Immunization Practices voted Thursday to recommend against using Merck & Co.'s combined measles, mumps, rubella and varicella vaccine in young children receiving their first dose, seeking to reduce the incidence of rare cases of seizures.
The committee voted 8-3, with one abstention, to recommend that the varicella shot be administered separately from the MMR inoculation in children age 4 and younger. Current policy allows either approach for the youngest children: MMR and varicella together in Merck's combined ProQuad vaccine, or in two separate shots.
Safety Data Drives Policy Shift
Panelists who advocated for the change pointed to data indicating the combined shot has around double the rate of fever-related, or febrile, seizures in this group of children — roughly seven to eight per 10,000 compared to roughly three to four per 10,000 for those receiving MMR and varicella separately at the same physician visit.
Committee member Vicky Pebsworth, research director for the vaccine skeptical group National Vaccine Information Center, argued that reducing febrile seizures could prove beneficial to public health. She noted how some research has shown "detrimental effects on neurodevelopment" that could make children susceptible to attention deficit hyperactivity disorder, epilepsy and other conditions.
However, committee member Cody Meissner, a pediatrics professor at Dartmouth College, disagreed with the significance of the risk. "Febrile seizures occur in 3% to 5% of all children. They're common, and every pediatrician is experienced in febrile seizures, and we know that the prognosis is excellent," he said.
Limited Practical Impact Expected
As a practical matter, such a policy shift may not prevent many febrile seizures. Because the CDC already evaluated this risk in 2008 and 2009, and communicated it to physicians and patients, only around 15% of children in this age group receive the four-part shot, CDC officials said.
"I'm not quite sure where we're going with this discussion," said Meissner. "I think that the current wording is appropriate."
Implementation Concerns and Coverage Issues
The combined shot improves adherence to the childhood vaccination schedule, which in turn helps prevent disease outbreaks, panelists opposed to changing the recommendation said. Moreover, changing guidelines could take away parents' options by reducing their access to the MMRV vaccine.
For example, the Vaccines For Children program may no longer be able to pay for the MMRV vaccine, although health insurers committed to covering any shot recommended as of Sept. 1 through the end of 2026.
Initial confusion arose when the committee voted 8-1, with three abstentions, to retain the program's coverage under the old CDC recommendations on Thursday. Committee members were unsure of the meaning of this second vote, wondering whether it would mean differing guidelines depending on how a child's vaccine was covered.
On Friday, the committee reconvened and agreed to re-do their vote, citing the previous day's confusion. Nine members voted to endorse adoption of the new guidelines in the Vaccines for Children program, while three abstained.
Political Context and Controversy
The tension over the MMR vaccine schedule is heightened by the role of Health and Human Services Secretary Robert F. Kennedy Jr. — a vaccine critic himself — in firing all the prior ACIP members in June and installing the current hand-picked panel. Kennedy also dismissed former CDC director Susan Monarez, who claims she was fired for refusing to rubber stamp ACIP recommendations ahead of time.
Jason Goldman, a liaison to the committee from the American College of Physicians, criticized the committee's handling of the issue. "I was very concerned about the vote that was taken yesterday, because you had two conflicting votes that you're now reconsidering," he said.
"Would you consider that the second vote [Thursday] actually revealed the truth, that you do not have the data or evidence to challenge the current standing and that there is no associated harm?" Goldman added.
Broader Vaccine Landscape
The MMR vaccine has long been in the crosshairs of anti-vaccination activists, based around the now-discredited work of British doctor Andrew Wakefield, who sought to link use of the MMR vaccine with increasing incidence of autism. Kennedy's HHS is expected to deliver a report this month on the causes of autism.
This year, the U.S. reported more measles cases than in any year in more than three decades, with 1,454 confirmed measles cases nationwide as of September 9. Combination vaccines to prevent infection with measles, mumps and rubella viruses are marketed in the United States by Merck and GSK, with Merck also selling the ProQuad shot that includes protection against those three viruses and varicella.
ACIP recommendations go to the CDC director for endorsement. With the recent ouster of former agency head Susan Monarez, acting director Jim O'Neill will likely be the official to review the recommendations.
