ACIP Recommends Clesrovimab for Infants Under 8 Months Without Maternal RSV Protection

The ACIP voted on two key RSV-related issues. First, whether to formally recommend the use of RSV monoclonal antibodies, Sanofi/AstraZeneca’s Beyfortus and Merck’s newly approved Enflonsia, for infants and young children to protect against RSV during their first (and potentially second) RSV season. Second, whether to include these antibody products in the Vaccines for Children (VFC) program, which would provide them at no cost to eligible families.

ACIP Vote 1

Infants under 8 months of age born during or entering their first RSV season, who are not protected by maternal vaccination, should receive 1 dose of clesrovimab.

Yes (5)

• Robert W Malone, MD
• Joseph R Hibbeln, MD, ABNP, CAPT USPHS (Ret.)
• James Pagano, MD, FACEP
• Cody Meissner, MD
• Martin Kulldorff, PhD

No (2)

• Retsef Levi, PhD
• Vicky Pebsworth, PhD, RN

ACIP Vote 2

Approve the updated Vaccines for Children (VFC) program resolution to include RSV prevention products, including clesrovimab.

Yes (7)

• Robert W Malone, MD
• James Pagano, MD, FACEP
• Cody Meissner, MD
• Joseph R Hibbeln, MD, ABNP, CAPT USPHS (Ret)
• Retsef Levi, PhD
• Vicky Pebsworth, PhD, RN
• Martin Kulldorff, PhD

Meeting Notes

CDC Work Group Recommends Clesrovimab (Enflonsia) to Protect Infants Under 8 Months From RSV

The CDC’s Maternal/Pediatric RSV Work Group has issued a strong recommendation for the use of clesrovimab, a long-acting monoclonal antibody, to prevent severe respiratory syncytial virus (RSV) disease in all infants under 8 months of age entering their first RSV season.

High Burden of RSV in Young Infants

RSV remains a leading cause of respiratory illness in children under five, accounting for approximately 2 million medical visits, up to 80,000 hospitalizations, and hundreds of deaths annually in the United States. Infants younger than 8 months are especially vulnerable, with hospitalization rates between 2-3%, predominantly affecting otherwise healthy infants.

Proven Efficacy and Safety

Clinical trial data demonstrate that clesrovimab reduces RSV-related hospitalizations by over 90% and lowers the risk of medically attended RSV lower respiratory tract infections by 60%. The antibody’s safety profile is favorable, with serious adverse events rare and comparable to placebo. Minor side effects such as irritability or sleepiness were mild and infrequent.

Implementation and Access

Clesrovimab offers a simplified, single-dose regimen regardless of infant weight, facilitating administration during birth hospitalization or early in the RSV season. The CDC highlights that inclusion in the federally funded Vaccines for Children (VFC) program would enhance equitable access and uptake.

While some providers may face challenges managing inventory alongside other RSV antibodies like nirsevimab, pediatricians surveyed remain confident in recommending monoclonal antibody RSV prevention, with many already offering similar therapies.

Cost-Effectiveness and Public Health Impact

Modeling estimates suggest that with 50% coverage, clesrovimab could prevent tens of thousands of RSV-related healthcare visits and approximately 20 deaths annually, gaining over 3,400 quality-adjusted life years. Although not cost-saving, the intervention is considered a reasonable and efficient allocation of healthcare resources at an estimated $105,000 per QALY gained.

Multiple Options Strengthen RSV Prevention

The work group emphasized the benefits of having multiple monoclonal antibody options, noting that additional products can mitigate risks related to supply shortages or viral resistance, potentially drive competitive pricing, and broaden protection for infants.

FDA Approval June 9, 2024

The US FDA has approved Enflonsia (clesrovimab), a single-dose, long-acting monoclonal antibody, to prevent RSV (respiratory syncytial virus) infections in infants during their first RSV season. The treatment significantly reduces RSV-related hospitalizations by 84.3% and medically attended infections by 60.5%.

Enflonsia offers a weight-independent dosing option for both preterm and full-term infants, providing a major advance in RSV prevention. Merck plans to make it available before the 2025–26 RSV season, expanding options beyond existing therapies like Sanofi and AstraZeneca’s Beyfortus.

Approval was based on results from the CLEVER phase 2b/3 trial, which showed strong efficacy and safety over 150 days. Additionally, the SMART phase 3 trial, which compared Enflonsia to palivizumab in high-risk infants, showed comparable safety and effectiveness. Enflonsia’s approval provides a new tool in reducing this burden and underscores the importance of monoclonal antibodies in pediatric respiratory care.

References

CDC. Advisory Committee on Immunization Practices (ACIP) - Day 2 of 2. June 26, 2025. Accessed June 26, 2025. https://www.cdc.gov/acip/meetings/index.html

US FDA Approves Merck’s ENFLONSIA™ (clesrovimab-cfor) for Prevention of Respiratory Syncytial Virus (RSV) Lower Respiratory Tract Disease in Infants Born During or Entering Their First RSV Season. Merck. Press release. June 9, 2025. Accessed June 26, 2025. https://www.merck.com/news/u-s-fda-approves-mercks-enflonsia-clesrovimab-cfor-for-prevention-of-respiratory-syncytial-virus-rsv-lower-respiratory-tract-disease-in-infants-born-during-or-entering-their-fir/