The Centers for Disease Control and Prevention’s Advisory Committee on Immunization Practices (ACIP) concluded a meeting this week with significant votes on childhood vaccination schedules, marking a dramatic departure from decades of established public health policy. The committee, entirely reconstituted by Health Secretary Robert F. Kennedy Jr., voted to restrict access to certain vaccines while postponing other controversial decisions amid widespread criticism from medical professionals.

On Thursday, ACIP voted 8-3 to recommend against the combined measles, mumps, rubella, and varicella (MMRV) vaccine for children under 4 years old. The committee cited concerns about a slightly elevated risk of febrile seizures in children aged 12-23 months compared to receiving separate MMR and varicella vaccines. The CDC has known about this risk for years, and currently, about 85% of parents still opt for separate MMR and varicella vaccines for the first dose to reduce the risk, according to data presented at Thursday’s ACIP meeting.

The vote was followed by a second decision on Friday to align the Vaccines for Children (VFC) program with this new recommendation, meaning the combination shot will no longer be covered for low-income families, though separate MMR and varicella vaccines will remain available.

The MMRV vaccine, which protects against measles, mumps, rubella, and varicella (chickenpox), was developed to combine the existing MMR vaccine (measles, mumps, rubella) with the varicella (chickenpox) vaccine into a single shot. The combined MMRV vaccine was first licensed for use in the United States in 2005, making it possible for children to receive protection against all four diseases with fewer injections.

The vaccine was created to simplify childhood immunization schedules and increase vaccination rates by reducing the total number of shots needed. By combining the MMR and varicella vaccines, healthcare providers could offer comprehensive protection with a single injection, lowering the burden on families and medical staff.

The MMR vaccine had already existed since 1971, and standalone varicella vaccines became available in the 1990s. Combining them as MMRV followed when safety, efficacy, and immunogenicity were established for the four-in-one format.

Measles, mumps, rubella, and varicella (chickenpox) can each cause serious and sometimes lifelong consequences, especially in unvaccinated populations and vulnerable groups.

Measles

• Measles can lead to pneumonia, encephalitis (brain swelling), deafness, intellectual disability, and even death.
• One life-threatening long-term complication is subacute sclerosing panencephalitis (SSPE), a progressive, fatal brain disease that may appear 7–11 years after infection.
• Measles causes “immune amnesia,” erasing immune memory and leaving children vulnerable to other serious infections for years after recovery.

Mumps

• Mumps can result in deafness, meningitis (brain/spinal cord inflammation), encephalitis, and orchitis (swelling of the testicles), which may cause infertility.
• It may also cause oophoritis (ovary swelling), pancreatitis, and in rare cases, permanent neurological damage.

Rubella

• Rubella infection during pregnancy can cause congenital rubella syndrome, resulting in miscarriage, birth defects (such as deafness, heart defects, and cataracts), and intellectual disability.
• In children and adults, rubella may trigger arthritis or encephalitis (rarely).

Varicella (Chickenpox)

• Varicella can lead to pneumonia, encephalitis, severe skin infections, and dehydration.
• The virus remains dormant and may reactivate years later as shingles, which can cause chronic nerve pain (postherpetic neuralgia).
• In immunocompromised individuals, chickenpox can be severe or fatal.

Vaccination against all four diseases dramatically reduces these risks and has saved millions of lives by preventing severe complications and deaths.

The committee was originally scheduled to vote Thursday on delaying the first hepatitis B vaccine dose from birth to at least one month of age for infants born to mothers who test negative for the virus. However, members voted 11-1 to table this decision.

The hepatitis B discussion revealed deep divisions within the committee about the necessity of universal birth vaccination. Several members questioned decades of established policy despite CDC data showing the birth dose has reduced infant hepatitis B cases by 99% since 1991.

Kennedy dismissed all 17 previous ACIP members in June 2025, claiming they were “burdened with ongoing conflicts of interest,” despite no evidence supporting this assertion. An independent analysis found that conflicts of interest had actually reached “historically low levels” before the panel was disbanded.

Kennedy initially appointed 8 new members in June, then added 5 more just days before this week’s meeting, bringing the total to 12 members. Many appointees have histories of vaccine skepticism or spreading medical misinformation.

The American Academy of Pediatrics withdrew from participating in ACIP meetings and issued its own vaccine recommendations, breaking with federal guidance.