RSV Prevention Today and Tomorrow: Reducing Infant Hospitalizations 

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 By Debonique Burton

Respiratory Syncytial Virus (RSV) is a very common respiratory virus that in most patients often presents with cold-like symptoms such as fever, sneezing, runny nose, cough, and/or decreased appetite.​ Unfortunately, in infants and those with risk factors for severe disease, can cause more serious illness such as bronchiolitis and pneumonia.  RSV has been the most common cause of hospital admissions among infants in the United States, leading to approximately 50,000 to 80,000 hospitalizations each year in children younger than five.​1,2​  Data from the Respiratory Syncytial Virus (RSV) Hospitalization Surveillance Network (RSV-NET ~300 hospitals in 16 states) and the New Vaccine Surveillance Network (NVSN outpatient networks in 7 US sites), surveillance networks showed a significant reduction of RSV-related hospitalizations in children under 5 years old from 11,581 in 2018-2020 to 6,708 in 2024-2025.​3​  Specifically, this was a reduction of 28% based on NVSN data and 43% based on RSV-NET data after  the introduction of preventative RSV immunizations.​3 The authors also noted month by month reductions for those 0–7 months during the RSV immunization roll out, further evidence supporting that the change was most likely due to RSV immunizations.​3

 

Options to Protect Infants Against RSV

RSV immunizations were introduced in the fall of 2024 and included RSV vaccine RSVpreF (Abrysvo, the only RSV vaccine FDA-approved for pregnant patients) and infant monoclonal antibody nirsevimab (Beyfortus). More recently, clesrovimab (Enflonsia), another infant monoclonal antibody has become FDA approved and recommended as another option to protect infants against severe RSV lower respiratory.4-6​

 

Impact of RSV Immunization in Infants

The 2024–2025 RSV season was the first in the U.S. with widespread use of both the maternal RSV vaccine and nirsevimab. Data from the National Immunization Survey showed that the percentage of U.S. infants aged 0–7 months protected by either approach (i.e., maternal vaccination or infant monoclonal antibody administration) rose from 30% in October 2024 to 66% by February 2025. This increase coincided with significant declines in RSV-related hospitalizations. The decrease was even more noticeable when excluding Houston, where prevention products were not widely available early in the season​.3​ The real-world drop in hospitalizations aligns with clinical trials which reported 80% efficacy of nirsevimab and about 70% efficacy of Abrysvo for preventing hospitalization among young infants.2,7,8

Data from the phase 3 trial which included 901 infants up to 1 year of age, evaluated the safety, efficacy, and pharmacokinetics of clesrovimab in infants and children at increased risk for severe RSV disease reported that clesrovimab reduced the risk of RSV-related hospitalization for lower respiratory tract infection by about 91% compared to the control group [95%CI, 90.9 (76.2, 96.5)]​​.10  Clesrovimab was found to be well tolerated in infants considered at high risk for RSV. The most frequently reported side effects of clesrovimab included redness at the injection site (3.8%), swelling at the injection site (2.7%), and rash (2.3%)​​.1,10

 

Recommendations for RSV Immunization

It is recommended that pregnant individuals between 32 and 36 weeks 6 days gestation, if not previously vaccinated against RSV, should receive RSVpreF vaccine September through January.6,9  In cases when the mother did not receive the RSVpreF or receive it less than 14 days prior to delivery their infants < 8 months old are recommended to either nirsevimab or clesrovimab monoclonal antibody between October and March either at discharge from the hospital or at the first available visit in this timepoint.4,5,9   There are also some high-risk infants and young children (i.e., those 8-19 months old) with specific risk factors for severe RSV disease including those who have chronic lung disease of prematurity (and receiving steroids, diuretics, or oxygen within the past 6 months), severe immunocompromise, cystic fibrosis or are American Indian or Alaska Native.4,5,9 These high-risk individuals should receive nirsevimab just prior to the beginning of their second RSV season.4,5,9​  At this time, there is not currently a preference for one method over another.

 

Summary – Infant RSV Immunization Recommendations4-6

Immunization Product Recommendations Dosing
Maternal Vaccination

Abrysvo (RSVpreF)

 Pregnant individuals who have not yet received any RSV vaccine should receive a single dose of Abrysvo (RSVpreF) between 32 and 36 weeks, 6 days gestation, preferably from September through January in most areas of the U.S. All: 0.5 mL IM
Infant Immunization with Monoclonal Antibody

 Beyfortus (Nirsevimab) or Enflonsia (Clesrovimab)

 Recommended from October through March (in most areas of the U.S.):

• Infants <8 months whose mother did not receive RSVpreF ≥14 days before birth during this pregnancy should receive either nirsevimab or clesrovimab.

• Children 8–19 months at higher risk for severe RSV should receive nirsevimab.

 Nirsevimab:

• <8 months: 50 mg or 100 mg IM (depending on weight)

• 8–19 months: 200 mg IM

Clesrovimab:

• 105 mg IM

 

About the author: Debonique Burton is a Doctor of Pharmacy candidate at the University of Connecticut. This post was written as part of her Advanced Pharmacy Practice Experience under the guidance of her professor, Jennifer Girotto PharmD, BCPPS, BCIDP, who also reviewed and edited the piece.

 

References

  1. Maternal/Pediatric Work Group of the Advisory Committee on Immunization Practices. Evidence to Recommendation Framework: Clesrovimab. Accessed July 9, 2025. Available at: https://www.cdc.gov/acip/downloads/slides-2025-06-25-26/05-MacNeil-Mat-Peds-RSV-508.pdf
  2. Moline HL, Tannis A, Toepfer AP, et al. Early Estimate of Nirsevimab Effectiveness for Prevention of Respiratory Syncytial Virus-Associated Hospitalization Among Infants Entering Their First Respiratory Syncytial Virus Season – New Vaccine Surveillance Network, October 2023-February 2024. MMWR Morb Mortal Wkly Rep. 2024;73(9):209–214.
  3. Patton ME, Moline HL, Whitaker M, et al. Interim Evaluation of Respiratory Syncytial Virus Hospitalization Rates Among Infants and Young Children After Introduction of Respiratory Syncytial Virus Prevention Products – United States, October 2024-February 2025. MMWR Morb Mortal Wkly Rep. 2025;74(16):273–281.
  4. American Academy of Pediatrics, Committee on Infectious Diseases. Red Book: Report of the Committee on Infectious Diseases 2024 – 2027. Immunization Schedules. Accessed September 20, 2025. Available at: https://publications-aap-org.ezproxy.lib.uconn.edu/redbook/book/755/Red-Book-2024-2027-Report-of-the-Committee-on
  5. Centers for Disease Control and Prevention. Child and Adolescent Immunization Schedule by Age (Addendum updated July 2, 2025). Accessed September 20, 2025. Available at: https://www.cdc.gov/vaccines/hcp/imz-schedules/child-adolescent-age.html
  6. Centers for Disease Control and Prevention. Adult Immunization Schedule by Age (Addendum updated July 2, 2025). Accessed September 20, 2025. Available at: https://www.cdc.gov/vaccines/hcp/imz-schedules/adult-age.html
  7. Alandijany TA, Qashqari FS. Evaluating the efficacy, safety, and immunogenicity of FDA-approved RSV vaccines: a systematic review of Arexvy, Abrysvo, and mResvia. Front Immunol. 2025;16:1624007.
  8. Simões EAF, Pahud BA, Madhi SA, et al. Efficacy, Safety, and Immunogenicity of the MATISSE (Maternal Immunization Study for Safety and Efficacy) Maternal Respiratory Syncytial Virus Prefusion F Protein Vaccine Trial. Obstet Gynecol. 2025;145(2):157–167.
  9. American Academy of Pediatrics, Committee on Infectious Diseases. AAP Recommendations for the Prevention of RSV Disease in Infants and Children. In: AAP Recommendations for the Prevention of RSV Disease in Infants and Children Red Book : Report of the Committee on Infectious Diseases 2024 – 2027.
  10. Heather J Zar &, Louis J Bont, Paolo Manzoni M, et al. Phase 3, Randomized, Controlled Trial Evaluating Safety, Efficacy, and Pharmacokinetics (PK) of Clesrovimab in Infants and Children at Increased Risk for Severe Respiratory Syncytial Virus (RSV) Disease. 2025;Volume 12 (supplement 1).