CDC Committee No Longer Recommends MMRV Vaccine for Children Under Four

The U.S. Centers for Disease Control and Prevention’s (CDC) Advisory Committee on Immunization Practices (ACIP) met on Sept. 18-19, 2025 to review recommendations on childhood vaccines, including the combined live virus measles, mumps, rubella, and varicella (MMRV) shot, marketed under the brand name ProQuad®. In a notable shift, the panel voted not to recommend the MMRV vaccine for children under age four, citing a higher risk of fever-related seizures in toddlers. Under prior guidance, parents could opt for their young children to receive  the combined MMRV shot rather than receiving the MMR and varicella zoster (chicknpox) vaccines separately.  The updated guidance keeps the combined MMRV vaccine acceptable for the second dose at ages 4–6, when seizure risk is no longer elevated.¹

The ACIP, which underwent a recent restructuring with new members appointed by Secretary of Health and Human Services Robert F. Kennedy, Jr,  also revisited its position on whether the MMRV shot should remain covered under the federal Vaccines for Children (VFC) program. The panel ultimately voted to remove it. The VFC is a federally funded insurance program created by Congress in the 1990s that provides recommended vaccines at no cost to eligible uninsured and underinsured children, who may otherwise be unable to afford to get vaccinated.

While the ACIP vote effectively limits access to the combined MMRV vaccine for uninsured or underinsured families, ACIP members noted that the VFC program is designed to provide free vaccines only when they are consistent with official CDC vaccine use recommendations. Supporters of the change argued that this alignment is important to avoid funding products no longer considered the safest option for young children.^{1 2}

Concerns About Combo Vaccines Versus Co-Administration of Separate Vaccines

The ACIP’s decision on the MMRV vaccine comes as the FDA is re-evaluating long-standing guidance on giving multiple vaccines to children in the same time. In a recent FDA memo, leadership at the Center for Biologics Evaluation and Research (CBER) said the agency “cannot affirm” the safety or effectiveness of concurrent administration of vaccines without new randomized clinical trials, particularly for pairings such as COVID-19 and influenza, and announced that additional studies will be required before manufacturers can continue to market claims  for safety and effectiveness.³

Both combo vaccines (single shots that contain multiple antigens) and co-administration of separate shots have been shown to increase the likelihood of side effects compared with spacing doses out over time. Combo vaccines are widely used in childhood vaccination schedules—these include DTaP (diphtheria, tetanus, acellular pertussis), DTaP-IPV/Hib (adding polio and Haemophilus influenzae type b), MMR (measles, mumps, rubella), and MMRV (which adds varicella/chickenpox). These formulations reduce the number of injections but also change the overall reactogenicity profile.

Studies have documented higher rates of cases of fatigue, headache, and muscle aches when COVID-19 and flu shots are given together, as well as increased early fever when influenza (TIV) and pneumococcal (PCV13) vaccines are co-administered in young children.⁴

As for the MMRV vaccine specifically, the focus of ACIP’s vote, multiple cohort analyses and ACIP’s own review show a higher risk of febrile seizures after the first MMRV dose at 12–23 months compared with giving MMR and varicella as two separate injections at the same visit. The ACIP says no increased risk is seen for the second dose at ages four to six years old  This product-specific safety signal—rather than the FDA’s broader concerns about co-administration, which have shown similar acute side effects—was the direct basis for ACIP’s new recommendation.¹

A separate vote on whether to delay the routine hepatitis B birth dose was postponed, with members citing the need for more information before making changes.¹

MMRV Trial Participants Only Monitored for 42 Days After Vaccination

In pre-licensure clinical trials for Merck’s ProQuad® (MMRV), participant were monitored for only 42 days after vaccination.  Health outcomes of those who received MMRV were compared to children who received MMR and Varivax separately, rather than comparing MMRV to those who received an inert placebo. This made it virtually impossible to isolate ProQuad-specific reaction risks, since both groups were exposed to live-virus vaccines with overlapping side-effect profiles.⁵

The ProQuad® package insert acknowledges a higher rate of febrile seizures in children 12 to 23 months old after the first dose, and post-marketing reports describe rare but serious events such as encephalitis, meningitis, anaphylaxis, Guillain-Barré syndrome (GBS), and Stevens-Johnson syndrome. Because some conditions, including immune-mediated disorders, can emerge weeks or months later, adverse events occurring beyond the 42-day observation period may not have been captured in pre-licensure safety data.⁵

The MMRV product insert also warns that live varicella vaccine virus may be shed from vaccine recipients who develop a rash, potentially transmitting infection to susceptible close contacts, including immunocompromised individuals, debunking the widespread belief that vaccination guarantees prevention of viral infection and transmission.⁵

2010 Study Found Seizure Risk Nearly Doubled

While widespread media coverage of ACIP’s latest guidance on the MMRV vaccine has downplayed or minimized the elevated risk of febrile seizures linked to the combo vaccine, a large 2010 study analyzing Vaccine Safety Datalink data found that children who received MMRV had nearly double the risk of febrile seizures compared with those who received MMR and varicella separately (relative risk: 1.98, meaning the chance of a seizure was almost twice as high in the MMRV group). The authors noted that “vaccination with MMRV results in one  additional febrile seizure “for every 2,300 doses given” and emphasized that MMR vaccines themselves—used as a placebo in MMRV clinical trials—already carry a seizure risk, which the combination vaccine amplifies. Although the individual risk may appear small, it becomes significant when scaled to millions of children.⁶

The 2010 Pediatrics study that confirmed a doubled seizure risk was designed to evaluate only fever and seizure outcomes, not other adverse events. This narrow focus means that other conditions documented on the product insert—such as encephalitis, thrombocytopenia, or Stevens-Johnson syndrome—would not have been systematically captured, leaving open questions about elevated risks of adverse events beyond febrile seizures. As the authors themselves noted, “we did not assess other rare adverse events.”⁶

Fifteen Years Between Risk Signal and Policy Shift

Merck said in a statement that the ACIP’s discussion and votes “occurred in the absence of new scientific data and in contrast to years of evidence affirming the current immunization schedule.” The drug maker criticized the panel’s vote, citing that “the resulting decision poses significant risk to public health — from undermining public confidence in vaccination programs to potentially increasing the burden of vaccine‑preventable disease in our communities.”⁷

Notably, ACIP was first alerted to preliminary evidence of a doubled seizure risk back in 2008, but did not revise its recommendations at that time. Merck, the sole manufacturer of MMRV (ProQuad®), continued to market the vaccine, and the 2010 study disclosing the risk also noted that two lead investigators had received research funding from vaccine manufacturers, including Merck. It took more than 15 years after the risk was first identified for the ACIP to formally revise its recommendations.⁶

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