Pediatric RSV Prevention Gets an Upgrade in Nirsevimab

Written by Ardis M. Copenhaver, PharmD, MS, BCPS

Respiratory syncytial virus (RSV) is a respiratory virus that usually causes cold-like symptoms and tends to occur between the beginning of October and end of March in the United States.(1) It is the most common cause of lower respiratory tract infections in children younger than 1 year of age and the leading cause of hospitalization among infants.(1) The highest rate of hospitalizations occurs during the first months of life with risk declining alongside increasing age.(1) Beyond hospitalizations, RSV contributes to a significant burden on the health care system by increasing outpatient visits, emergency department use, and seasonal strain on health care resources.

What is Special About Nirsevimab?

Until recently, our prevention strategy relied on palivizumab, a monoclonal antibody with a 20-day half-life, administered monthly to high-risk pediatric patients during RSV season.(1-3) This left a large population of otherwise healthy infants and children vulnerable to RSV and its severe complications.(1) In July 2023, the Food and Drug Administration (FDA) approved nirsevimab, a monoclonal antibody with an extended half-life of 71 days to prevent RSV lower respiratory tract infection (LRTI) in neonates, infants and certain children who remain vulnerable to severe RSV infection.(1, 2) Subsequently, in August 2023, the Centers for Disease Control and Prevention’s (CDC) Advisory Committee on Immunization Practice (ACIP) recommended nirsevimab over palivizumab in eligible infants and children due to its long-acting efficacy after a single dose.(1, 2) The CDC recommends administering nirsevimab to infants <8 months to protect against RSV-associated LRTI shortly before or during their first RSV season and for children 8 to 19 months at risk for severe RSV disease for their second RSV season.(1, 2)

What is the Clinical Efficacy and Safety?

The FDA approval for nirsevimab was supported by several clinical trials, where the primary end point was the incidence of medically attended RSV LRTI occurring in the 150 days after administration.(1,4,5) One of the initial trials evaluated healthy infants who had been born preterm (29 weeks to <35 gestation). The study had a total of 1453 infants undergoing a 2:1 randomization (969 nirsevimab group and 484 placebo group) to receive nirsevimab or placebo at the start of an RSV season.(1,4,5) The nirsevimab group demonstrated a lower incidence of the primary end point compared to placebo (2.6% [25 infants] vs 9.5% [46 infants] 95% confidence interval [CI] 52.3 to 81.2; P<0.001) with an efficacy of 70.1%. (4,5)

Another trial, the MELODY Study, had a total of 1490 infants undergoing a similar randomization (994 nirsevimab group and 496 placebo group) in healthy late-term and term infants (gestational age of >35 weeks) entering their first RSV season.(1,4,5) The nirsevimab group demonstrated a lower incidence of primary end point compared to placebo (1.2% vs 5.0%; 95% CI, 49.6 to 87.1; P<0.001) with an efficacy of 74.5%.(5,6)

The adverse events of nirsevimab were similar between the two study groups in both trials and consistent with many other injectable medications.(1, 4-6) The most reported adverse effects include fever, rash, or local injection site reaction.(3-5) Common warnings among other monoclonal antibodies (human immunoglobulin G1 (IgG1) include hypersensitivity reaction.(1,3,5)

Are There Any Special Circumstance for Administering Nirsevimab?

The ACIP and American Academy of Pediatrics (AAP) recommend one dose of nirsevimab for all infants <8 months born during or entering their first RSV season whose pregnant parent did not receive the maternal RSV vaccine, who’s RSV vaccine status is unknown, or are born <14 weeks after the maternal RSV vaccine was administered (Table 1).(2) Additionally, one dose of nirsevimab is recommended for infants and children ages 8 to 19 months who are at increased risk for severe RSV disease and entering their second RSV season, regardless of RSV vaccination status of the pregnant parent (Table 1 and 2).(2) Ultimately, any child >20 months, who likely already experienced two RSV seasons and has been infected with RSV are less likely to benefit. Therefore, nirsevimab is not recommend beyond this age.(1,5) Additional dosage recommendations are available for infants and children undergoing cardiac surgery with cardiopulmonary bypass.(1,5)

Table 1. Recommended dosage of nirsevimab for the first season in infants and second RSV season for children who remain at increased risk for severe RSV (IM=intramuscular) (1,2,5,7)

Table 2. List of conditions for infants and children who remain at increased risk of severe RSV disease and entering their second RSV season, regardless of RSV vaccination status of the pregnant parent (1,2,5,7)

How Should Nirsevimab be Stored and Administered?

Nirsevimab must be stored at refrigerated temperatures between 36F to 46F (2C to 8C).  After removal from the refrigerator and coming to room temperature [68F to 77F (20C to 25C)], Nirsevimab must be used within 8 hours or discarded.(5) Nirsevimab must be administered by intramuscular injection, preferably in the anterolateral aspect of the thigh and avoiding the gluteal muscle.(4-6) If two injections of nirsevimab are required, administer in a different injection site.(4-6) It is safe and effective to give nirsevimab concomitantly with childhood vaccines in separate syringes and at different injection sites.(1,5,7)

Bottom Line

Nirsevimab marks a significant advancement in RSV prevention by providing season-long protection to all infants with a single dose.

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1. Jones JM, Fleming-Dutra KE, Prill MM, et al. Use of nirsevimab for the prevention of respiratory syncytial virus disease among infants and young children: recommendations of the Advisory Committee on Immunization Practices – United States, 2023. MMWR Morb Mortal Wkly Rep. 2023; 72 (34): 920-925.

2. AAP Recommendation for the Prevention of RSV Disease in Infants and Children. Red Book Online. 21 February 2024. https://publications.aap.org/redbook/resources/25379/AAP-Recommendations-for-the-Prevention-of-RSV?autologincheck=redirected. Accessed 10 April 2025.

3. Synagis® [package insert]. Sobi; 2020.

4. Griffin MP, Yuan Y, Takas T et al. Single-Dose Nirsevimab for Prevention of RSV in Preterm Infants. N Engl J Med. 2020; 282 (5): 415 – 425.

5. Beyfortus® [package insert]. Sanofi and AstraZeneca; 2023.

6. Hammitt L, Dagan R, Yuan Y et al. Nirsevimab for Prevention of RSV in Healthy Late-Preterm and Term Infants. N Engl J Med. 2022; (386 (9): 837- 846.

7. Nirsevimab Administration Visual Guide. American Academy of Pediatrics. Updated 10 September 2024. https://downloads.aap.org/AAP/PDF/Nirsevemab-Visual-Guide.pdf. Accessed 10 April 2025.

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Ardis M. Copenhaver, PharmD, MS, BCPS

Clinical Pharmacy Specialist

St. Clair Health, Pittsburgh, Pennsylvania