Healthcare Providers: RSV Immunization for Infants and Young Children

About Infant RSV Antibody

Infant RSV antibody products are injectable monoclonal antibodies that prevent severe RSV disease in infants and some young children. Monoclonal antibodies do not activate the immune system, as would occur with infection or vaccination (active immunization). Rather, the antibodies themselves protect against disease (passive immunization).

Because infant RSV antibodies do not activate the immune system, protection is likely most effective in the weeks after they are given and wanes over time. RSV antibodies do not provide long-term immunity to RSV disease but instead provide protection to infants in the 5 months after administration, when they are most at risk of getting severe RSV disease. As children get older, they are less likely to get severe symptoms from RSV infection.

There are two infant RSV antibody products available: clesrovimab and nirsevimab. Either product is recommended for use in infants younger than 8 months born during or entering their first RSV season. There is no preferential recommendation for use of these products in this age group. For children ages 8 through 19 months who are at increased risk of severe RSV disease and entering their second RSV season, only nirsevimab is recommended.

Storage and Handling of Infant RSV Antibody

Proper storage and handling of infant RSV antibody products is essential to ensure they are effective in preventing severe RSV disease. Nirsevimab and clesrovimab are both supplied as pre-filled syringes.

Pre-filled nirsevimab or clesrovimab syringes should be stored refrigerated between 36°F to 46°F (2°C to 8°C). They should be stored in the original carton to protect from light until time of use. Do not freeze, shake, or expose to heat.

Nirsevimab may be kept at room temperature 68°F to 77°F (20°C to 25°C) for a maximum of 8 hours. After removal from the refrigerator, nirsevimab must be used within 8 hours or discarded. Do not use nirsevimab beyond the expiration date printed on the label.

Clesrovimab may be kept at room temperature 68°F to 77°F (20°C to 25°C) for a maximum of 48 hours. After removal from the refrigerator, clesrovimab must be used within 48 hours or discarded. Do not use clesrovimab beyond the expiration date printed on the label.

Administering Infant RSV Antibody

Route

Administer infant RSV antibody intramuscularly. The preferred site of administration is the anterolateral thigh region for both clesrovimab and nirsevimab. Do not administer infant RSV antibody intravenously, intradermally, or subcutaneously.

Dosage

For nirsevimab:

• Age less than 8 months
  • 50 mg for infants weighing <5 kg [<11 lb], administered as single dose
  • 100 mg for infants weighing ≥5 kg [≥11 lb], administered as single dose
• Age 8 through 19 months
  • 200 mg, administered as two 100 mg injections

For clesrovimab:

• 105 mg/0.7 mL - Same dose for all infants younger than 8 months regardless of weight. Not recommended for infants 8 months of age and older.

Seasonal administration

See “Additional Considerations” in RSV Immunization Guidance for Infants and Young Children for more information on seasonal administration of RSV antibody.

Administration with Vaccine Products

Infant RSV antibody products can be administered without regard to timing of routine childhood vaccines. This includes simultaneous administration (i.e., same clinic day) with vaccine products. No interval between RSV antibodies and live vaccines (such as MMR and varicella) is necessary.

There is limited experience with administering infant RSV antibody with vaccine products. However, infant RSV antibody is not expected to interfere with the immune response to vaccine products. In clinical trials, when RSV antibody was given concomitantly with routine childhood vaccines, the safety and reactogenicity profile of the co-administered regimen was similar to the childhood vaccines given alone.

References

• 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;72:920–925. DOI: http://dx.doi.org/10.15585/mmwr.mm7234a4.
• Food and Drug Administration. Beyfortus (nirsevimab-alip) product label. Silver Spring, MD: US Department of Health and Human Services, Food and Drug Administration; 2023. https://www.accessdata.fda.gov/drugsatfda_docs/label/2024/761328s005lbl.pdf
• Food and Drug Administration: FDA Approves First Vaccine for Pregnant Individuals to Prevent RSV in Infants. Press Release. Silver Spring, MD: US Department of Health and Human Services, Food and Drug Administrations; 2023.
• Hamid S, Winn A, Parikh R, et al. Seasonality of Respiratory Syncytial Virus - United States, 2017-2023. MMWR Morb Mortal Wkly Rep. 2023 Apr 7;72(14):355-361. doi: 10.15585/mmwr.mm7214a1
• CDC RSV Surveillance & Research