Thread by @AnciraBecky

Overview of the ACIP Meeting on September 18-19, 2025
The U.S. Centers for Disease Control and Prevention’s (CDC) Advisory Committee on Immunization Practices (ACIP) held its virtual meeting on September 18-19, 2025, focusing on updates to vaccine recommendations, particularly those affecting pediatric and adult immunization schedules. The committee, recently reconstituted under Health and Human Services Secretary Robert F. Kennedy Jr., reviewed evidence on measles, mumps, rubella, and varicella (MMRV) vaccines, hepatitis B (Hep B) vaccines, and 2024-2025 COVID-19 vaccine implementation. Votes occurred primarily on Day 1 (September 18), with some deferred to Day 2. Discussions highlighted tensions between evidence-based safety data from CDC experts and skepticism from some ACIP members, leading to notable disarray, including confusion over vote wording and rationales.

The outcomes primarily impact pediatric vaccine schedules, emphasizing shared clinical decision-making (individualized risk-benefit discussions) over universal recommendations. No major changes were finalized for adult schedules on Day 1, though COVID-19 discussions continued. These recommendations, if adopted by the CDC Director, influence insurance coverage (e.g., no-cost sharing under the Affordable Care Act), Vaccines for Children (VFC) program eligibility, and pharmacy administration authority. However, America’s Health Insurance Plans (AHIP) stated that all ACIP-recommended immunizations as of September 1, 2025, will remain covered without changes, potentially buffering immediate access disruptions. Some states have also signaled they may not follow revised ACIP guidance.

Key Outcomes on Vaccine Schedules
1. MMRV Vaccine (Measles, Mumps, Rubella, and Varicella)
• Background: The combined MMRV vaccine (e.g., ProQuad) is currently recommended as an option for the first dose at 12-47 months to reduce injections, but ACIP has long advised separate MMR and varicella vaccines for the first dose due to a slightly elevated risk of febrile seizures (temporary, non-life-threatening events peaking at 14-18 months). Evidence presented showed the risk is about 1 extra seizure per 2,300-3,000 doses, with no long-term harm.
• Vote Outcome (September 18): ACIP voted to withdraw the recommendation for MMRV as the first dose in children under 2 years, mandating separate MMR and varicella vaccines instead. This passed by majority vote (exact tally not specified in real-time reports, but described as clear).

MMRV

• Rationale: Members cited seizure risks and “precautionary” concerns, despite CDC data affirming overall safety and efficacy. Some members expressed confusion over the data, questioning why the American Academy of Pediatrics (AAP) supports the combined option.
• Impact on Schedule:
• Pediatric schedule now requires two separate shots for the first dose (at 12-15 months), potentially increasing visits, costs, and hesitancy. MMRV remains an option for the second dose (at 4-6 years).
• Could reduce varicella (chickenpox) vaccination uptake, risking outbreaks and subsequent shingles surges in adults.
• VFC Coverage Vote: A follow-up resolution to adjust VFC funding for separate vaccines passed narrowly (1 yes, 8 no, 3 abstain to a proposed change), preserving current funding levels but sparking debate over interpretation—members post-vote asked for clarification on what they had approved.

MMRV

Broader Implications: Critics, including public health experts, argue this erodes trust and access, especially for low-income families reliant on VFC. AAP has indicated it may issue its own schedule, diverging from ACIP.

2. Hepatitis B Vaccine (Birth Dose)
• Background: Universal Hep B vaccination at birth (within 24 hours) has been standard since 1991 to prevent perinatal transmission, with >90% effectiveness in preventing chronic infection. Risks are minimal (e.g., no increased adverse events in neonates). The draft vote language proposed allowing the first dose at 1 month for infants of Hep B-negative mothers via shared decision-making.
• Vote Outcome: Deferred to September 19 due to ongoing debate. No final decision today, but discussions leaned toward relaxing the universal birth-dose mandate.
• Rationale: Some members questioned necessity for low-risk infants, citing transmission primarily via sex/needles later in life, despite evidence of undetected maternal infections and household risks. CDC experts emphasized the birth dose’s role in equity and outbreak prevention.

HEPATITIS B

• Potential Impact on Schedule (if approved tomorrow):
• Shift to 1-month minimum for low-risk infants, with birth dose retained only for high-risk cases (e.g., Hep B-positive mothers).
• Could increase Hep B incidence by 20-30% in unvaccinated infants, per modeling, disproportionately affecting underserved communities. Also exceeds ACIP’s scope by implying routine maternal testing, which isn’t ACIP’s purview.
• Broader Implications: If passed, this would mark the first major rollback of a core pediatric schedule element, potentially raising costs and access barriers if not covered as “routine.”

3. COVID-19 Vaccines (2024-2025 Updates)
• Background: Current schedule recommends mRNA vaccines (e.g., updated Pfizer/Moderna for KP.2 strain) for ages 6 months+, with Novavax as an alternative for 12+. Focus was on implementation, including pediatric access and non-mRNA options.
• Vote Outcome: No votes today; discussions centered on mRNA efficacy/safety data. A workgroup presentation emphasized mRNA platforms, alleviating concerns over Novavax access. Votes expected September 19.
• Rationale: Debates included booster timing and age thresholds (e.g., potential raise from 65+ to 75+ for routine flu/COVID combos), with members probing data on comorbidities in 65-74-year-olds.
• Impact on Schedule: Likely minor tweaks, such as clarified shared decision-making for children 6-17. Advocacy pushes for expanded Novavax in pediatrics amid mRNA “failures” (e.g., waning immunity).
• Broader Implications: In a politically charged environment, outcomes could influence adult uptake, but AHIP’s coverage pledge mitigates short-term changes.

Conclusion

Context and Reactions
This ACIP, with seven new members appointed by Kennedy (some vaccine-skeptical), faced criticism for perceived ideology over science—e.g., members repeatedly questioning settled data. Public comments (30 minutes allocated) urged evidence-based decisions, while liaisons like AAP boycotted workgroups in protest. Experts warn of downstream effects: lower immunization rates, outbreaks (e.g., measles up 20% in 2024), and eroded trust. The meeting webcast revealed “remarkable disarray,” with post-vote confusion underscoring rushed processes.
For full details, watch the archived webcast on CDC’s ACIP site or review slides at cdc.gov/acip/meetings/…. Updates from Day 2 (Hep B and COVID votes) will be posted on ClinicalTrials.gov and MMWR.