The US CDC’s vaccine advisory panel recommended changing the recommendation for most children being vaccinated for measles, mumps, rubella, and varicella, steering clinicians and parents away from a quadrivalent vaccine that is sometimes used as the first dose in the two-dose series.

No new evidence was presented, but eight members of the Advisory Committee on Immunization Practices (ACIP) voted that children under the age of 4 should not receive the MMRV vaccine (Proquad, Merck) because of a potential for febrile seizures. That potential side effect has been known since the vaccine was approved in 2005.

Three panelists voted against that new recommendation, while one, Robert W. Malone, MD, abstained, noting that he had been an expert witness against Merck in the past.

There was confusion when it came to voting on MMRV for the federally funded Vaccines for Children (VFC) program, which pays for ACIP-recommended vaccines for about half of children in the US. 

Chair Martin Kulldorff, PhD, voted to not recommend MMRV for children under age 4 in the VFC program, while eight panelists said the current recommendation should not be changed. Three ACIP members abstained.

“I’m not quite sure what I’m voting for here,” said Cody Meissner, MD, professor of pediatrics at Dartmouth Geisel School of Medicine, who abstained. “I don’t want discrepancy between the children who get their vaccine from VFC and the children who don’t get their vaccine through VFC. That’s not right,” he said.

Shortened Process?

The September 18 gathering was the second meeting of a newly constituted ACIP. Five members were added just days ahead of the meeting, while eight were named in a post on X in June, after HHS Secretary fired the previous 17 members. 

It was also the first ACIP meeting in which some 30 liaison groups — medical societies and public health and nursing organizations — did not assist in gathering evidence. In August, those groups were accused of being biased and were barred from formally participating, as reported by Medscape. 

The liaison organizations were still allowed to sit in and ask questions or offer opinions during the meeting. The American Academy of Pediatrics (AAP), among a few other organizations, however, chose not to participate.

The AAP’s CEO and executive vice president, Mark Del Monte, told Medscape Medical News in a statement that the current meetings “are not designed to be spaces for in-depth examination of the science; rather, those crucial conversations occur within the work groups — conversations in which AAP is no longer permitted to participate.”

Meissner said during the meeting that he was disappointed that AAP did not participate, calling it “a grave mistake,” and said the group “is moving themselves to irrelevance.” 

Two experts from the CDC presented data from postmarketing studies and a Cochrane review from 2021 on safety and effectiveness of the MMRV vaccine, including in comparison with children receiving separate dose 1 injections of MMR and varicella vaccines at the same visit.

Panelists had many questions — including about long-term safety — that CDC officials could not answer, in part, they noted, because they had only received very specific requests from Kulldorff.

CDC’s John Su, MD concluded that there was a slightly increased risk — about twofold higher — of febrile seizure 5-12 days after the first dose of MMRV in children aged 12-23 months compared to those getting the MMR vaccine.

Another CDC expert, Arjun Srinivasan, MD, told the panel that the majority — about 85% — of first doses are given separately. Only about 15% of first doses are MMRV.

The current ACIP recommendation is that for the first dose, given at 12 to 47-months, either MMR and varicella vaccine or MMRV may be used. Clinicians are advised to discuss the benefits and risks of both with parents or caregivers. For the second dose at age 15 months through 12 years, MMRV is generally preferred over separate injections. 

Srinivasan noted that since the vaccines for these diseases became available that there has been elimination of endemic measles, endemic rubella, a 99% decline in mumps cases and a 97% decline in varicella incidence.

Safety Questioned

Panelist Retsef Levi, PhD, professor of operations management at MIT Sloan School of Management, said he thought the seizures were being glossed over. “From a safety perspective, I’m very concerned when we just focus on what we measure, and we don’t try to get to understand the biological mechanisms that are taking place here,” he told the committee. “We don’t really know what’s going on.” 

Evelyn Griffin, MD, an ob-gyn at Baton Rouge General Hospital, Louisiana, and a panel member, said she wanted to see data on whether children who had seizures had long-term neurologic or learning deficits.

“Febrile seizures occur in 3%-5% of all children,” countered Meissner. “They’re common, and every pediatrician is experienced in febrile seizures, and we know that the prognosis is excellent,” he said, adding that there are no data showing that they were associated with developmental issues.

Steering patients away from the single-shot MMRV might reduce compliance, he said. 

And, said Meissner, by changing the current recommendation, “what we’re saying is we don’t trust parents to make a decision.”

The new recommendation “is going to create more confusion among the public,” Jason Goldman, MD, president of the American College of Physicians (ACP), told the panel. 

ACP was one of the liaison groups prohibited from contributing to the evidence-building process. “You do not have those subject-matter experts with the real-world experience to understand the implementation of these vaccines and the concerns of the patients,” said Goldman, noting ACP’s absence from the process.

And, he said, “You are taking away the choice of parents to have informed consent and discussion with their physician on what they want to do for the health and benefit of their children.”

The recommendations are not final until approved by the CDC director. Currently, there is no permanent director, so the task will fall to Acting Director Jim O'Neill, an investor who does not have a clinical or science background

Alicia Ault is a Saint Petersburg, Florida-based freelance journalist whose work has appeared in many health and science publications, including Smithsonian.com. You can find her on X @aliciaault and on Bluesky @aliciaault.bsky.social.