The acting CDC director has proposed splitting the MMR vaccine into three separate monovalent doses.

The CDC’s Advisory Committee on Immunization Practices (ACIP) recently updated its recommendations for childhood vaccinations and COVID-19 shots, resulting in more restricted access to certain vaccines. These changes align with vaccine skepticism that gained traction during the Trump administration.

This year, Health and Human Services Secretary Robert F. Kennedy Jr. reshaped ACIP, selecting individuals who have publicly questioned vaccine safety. Acting CDC Director Jim O’Neill has suggested dividing the measles, mumps, and rubella (MMR) vaccine into three separate vaccines that target one virus each.

In a post on X (formerly Twitter), O’Neill encouraged vaccine manufacturers to replace the combined MMR vaccine with individual vaccines for each virus. His statement mirrors a recent comment from President Trump, who posted on Truth Social advocating for the separation of the MMR vaccine into three distinct doses.

Currently, no monovalent vaccines for measles, mumps, or rubella are approved in the U.S., and the CDC has stated there is no scientific evidence supporting the split of the MMR vaccine into individual shots.

While it remains uncertain whether O’Neill’s proposal will be implemented, changes to the childhood vaccine schedule are already taking shape. In September, ACIP voted to revise the childhood vaccination schedule and limit COVID-19 vaccine recommendations.

Though these adjustments are relatively minor, they reflect the ongoing vaccine skepticism within the Trump administration and could have significant impacts on public health, vaccine access, and insurance coverage.

Robert F. Kennedy Jr. has committed to rebuilding public trust in vaccines and the CDC. In June, he dismissed all 17 members of ACIP and replaced them with individuals who have raised concerns about vaccine safety.

During two contentious days of meetings, ACIP members voted on changes to the MMR and hepatitis B vaccines without presenting new safety data to justify their decisions.

William Schaffner, MD, a professor of preventive medicine at Vanderbilt University, criticized the process, calling the lack of organization and reliance on anecdotal evidence troubling.

Charles Stoecker, PhD, a professor at Tulane University, noted that ACIP usually prepares thoroughly for these meetings, but this time there was no solid data presented. Instead, panel members discussed unverified reports, which Schaffner likened to “gossip.” He emphasized that scientific questions should be addressed with rigorous evidence, not rumors.

Changes to MMRV Vaccine Schedule

ACIP voted 8-3 to no longer recommend the combined MMRV vaccine for children under 4 years old. Parents can still choose to have their children receive the measles, mumps, and rubella (MMR) vaccine and the varicella vaccine separately.

This decision was based on data showing that the MMRV vaccine carries a slightly higher risk of febrile seizures compared to separate MMR and varicella shots. However, the overall risk of seizures remains low, and such seizures are typically not severe.

Jake Scott, MD, a clinical associate professor at Stanford Medicine, criticized the decision, arguing that it addressed a problem that didn’t exist. Parents already have the option to choose separate shots if they are concerned about febrile seizures.

Hepatitis B Vaccine Vote Postponed

ACIP also postponed a vote on potentially delaying the hepatitis B vaccine, which is currently administered at birth. The vote was delayed after contentious debates, with no new safety data provided to support any changes to the vaccine schedule.

Hepatitis B is a serious infection and a leading cause of liver cancer worldwide. The birth dose of the hepatitis B vaccine has been a major success in public health, but the Trump administration has questioned its necessity, suggesting that newborns don’t need the vaccine.

Changes to COVID-19 Vaccine Recommendations

ACIP also decided to end the universal recommendation for updated COVID-19 vaccines. The new guidance advises adults aged 65 and older to get vaccinated, but for people between the ages of 6 months and 64, the decision should be made in consultation with a healthcare professional.

A more extreme proposal that would have mandated prescriptions for COVID-19 vaccines narrowly failed in a tied vote, with the panel chair casting the deciding vote.

This shift has caused confusion among patients, healthcare providers, and pharmacies, as the new guidance depends on individual decision-making.

Potential Long-Term Effects of Vaccine Policy Shifts

While the changes to the MMRV and COVID-19 vaccine guidelines are unlikely to drastically affect vaccine access for most people, experts warn that they could signal more significant policy shifts in the future. The uncertainty surrounding these guidelines has raised concerns about future vaccine policies and their potential impacts on public trust, insurance coverage, and vaccination rates.

Charles Stoecker pointed out that loosening vaccine recommendations could reduce vaccine coverage and access. Experts also worry that the growing politicization of vaccine policy could create inconsistencies across states, undermining efforts to achieve nationwide immunity.

“Diseases don’t respect state lines,” said Jake Scott. “Viruses exploit every gap in population immunity.”