CDC Panel Rejects Merck's Childhood Combination Vaccine Schedule Change

On September 19, 2025, the influential U.S. Centers for Disease Control and Prevention (CDC) advisory committee voted against adopting a proposed change to the childhood immunization schedule. Led by Robert F. Kennedy Jr.'s hand-picked vaccine advisors, the panel recommended against administering Merck & Co.'s combined measles, mumps, rubella, and chickenpox vaccine (ProQuad) as a single shot to children under age 4. The primary concern cited was an increased risk of seizures associated with the combination vaccine in the youngest children, which can lead to temporary but serious health events.

The CDC panel suggested that infants should receive the components separately to minimize this risk, thus maintaining the safety standard for early childhood vaccinations. However, the panel agreed that ProQuad could still be used as the second dose in the recommended vaccination schedule.

This decision could potentially impact vaccine supply globally, as Merck manufactures all ProQuad, MMR, and chickenpox vaccines in the United States. The company has stated that an immediate switch to separate injections for all children could have widespread consequences. Merck maintains that there is no confirmed increase in seizure risk with ProQuad and cites studies showing that combination vaccines enhance health outcomes and reduce missed or delayed vaccinations.

Historically, the CDC has recommended separate injections for MMR and varicella vaccines for the first dose, which is administered around 12 months, to mitigate seizure risks. Nevertheless, only about 15% of children currently receive the combination shot at first vaccination.

The decision also sparked broader concerns about vaccine trust and safety, especially amid recent political shifts. Kennedy’s replacement of previous CDC panel members with new appointees, some of whom have echoed vaccine skepticism or have served as expert witnesses against vaccine manufacturers, has raised questions about the influence of political priorities on public health recommendations.

Despite the recommendation to keep ProQuad available in the federal vaccine program, the panel's authority to enforce access remains uncertain. Public health advocates and medical groups like the American Academy of Pediatrics have criticized these moves, arguing they might disrupt vaccination efforts and threaten herd immunity. Meanwhile, some states are issuing their own vaccine guidelines, opposing federal recommendations.

Industry representatives emphasize that the combination vaccine plays a crucial role in efficient immunization practices and maintaining high vaccination coverage, and they caution that altering current practices could have significant implications for vaccine availability and public health safety. For more information, source: MedicalXpress.