What to know
- To prevent severe RSV disease in infants, either maternal RSV vaccination (Pfizer's Abrysvo) or infant immunization with a long-acting RSV monoclonal antibody (nirsevimab or clesrovimab) is recommended. Most infants will not need both maternal vaccination and infant RSV antibodies.
- Administration of infant RSV antibody is recommended during October through March in most of the U.S. The optimal timing for infant RSV antibody administration is shortly before the RSV season begins (e.g., October–November), or within a baby's first week of life if born October through March (ideally during the birth hospitalization.)
- Infant RSV antibodies are highly effective in preventing RSV-associated hospitalization.
- Side effects are usually mild, such as pain, redness, or swelling where the injection was given, and resolve quickly. Hypersensitivity reactions are uncommon but have been reported with similar antibody products.
Overview
Nirsevimab and clesrovimab are monoclonal antibodies that prevent severe RSV disease and are recommended for infants. Nirsevimab is also recommended for some young children.
Monoclonal antibodies are not vaccines. They do not activate the immune system. Rather, the antibodies themselves protect against disease.
Healthcare providers should discuss both the RSV maternal vaccine (Pfizer’s Abrysvo) and infant RSV antibodies with parents and consider patient preferences when deciding which product is best for their patient's family.
Recommendations
Recommendation for infants
An infant RSV antibody is recommended for infants younger than 8 months of age who are born during or are entering their first RSV season (typically fall through spring) if:
- The mother did not receive RSV vaccine during pregnancy, or
- The mother’s RSV vaccination status is unknown, or
- The infant was born within 14 days of maternal RSV vaccination.
The child's age on the day the infant RSV antibody is administered should be used to determine if the child is eligible for immunization. Except in rare circumstances, an infant RSV antibody is not needed for most infants who are born 14 or more days after their mother received RSV vaccine.
Providers should talk to parents and recommend an infant RSV antibody for eligible babies. Ideally, babies born during October through March receive an infant RSV antibody during their birth hospitalization. However, administration can occur during any visit to a healthcare setting, including well-child visits.
For infants eligible for RSV antibody with prolonged hospitalizations shortly before or during the RSV season, providers may consider administering RSV antibody during the hospitalization to prevent healthcare-associated RSV disease. This decision should be based on clinical judgment weighing the potential risks and benefits.
Recommendation for some young children
Nirsevimab is recommended for some children (ages 8–19 months) who are at increased risk for severe RSV disease and entering their second RSV season.
The following children ages 8–19 months are recommended to get nirsevimab shortly before or as early as possible during their second RSV season:
- Children with chronic lung disease of prematurity who required medical support (chronic corticosteroid therapy, diuretic therapy, or supplemental oxygen) any time during the 6-month period before the start of the second RSV season
- Children with severe immunocompromise
- Children with cystic fibrosis who have either 1) manifestations of severe lung disease (previous hospitalization for pulmonary exacerbation in the first year of life or abnormalities on chest imaging that persist when stable), or 2) weight-for-length <10th percentile
- American Indian or Alaska Native children
Children ages 8 months and older who are not at increased risk of severe RSV disease should not receive an infant RSV antibody. CDC does not currently recommend nirsevimab for anyone aged 20 months or older.
Clesrovimab is not recommended for children over 8 months of age and does not have FDA approval for children entering their second RSV season.
The American Academy of Pediatrics (AAP) publishes recommendations for palivizumab, including considerations for use of palivizumab in the setting of nirsevimab recommendations. Starting December 31, 2025, palivizumab will no longer be available.
Additional considerations
Seasonal administration
Infant RSV antibodies should be administered October through the end of March in most of the continental United States.
Infants born during the seasonal administration window (October 1 through March 31) should get an infant RSV antibody within one week after birth - ideally during the birth hospitalization. Throughout March, any eligible infant or young child who has not yet received a recommended dose should receive an infant RSV antibody at the earliest opportunity.
For infants born outside of the seasonal administration window (which is April through September) and for young children who are at increased risk for severe RSV disease and entering their second RSV season, the optimal timing for infant RSV antibody administration is shortly before the RSV season begins (e.g., October or November).
Additionally, because the timing of RSV activity varies geographically in other regions of the U.S., public health authorities may elect to provide revised guidance regarding the timing of RSV antibody administration based on local epidemiology and feasibility of implementation, including beginning administration prior to October or continuing beyond March or extending or shortening the administration period. Public health authorities should consider the advantages and disadvantages of modifying the timing of administration. Providers, including regional medical centers and health systems, should consult with state or territorial health departments prior to systematically modifying months of RSV antibody administration for their eligible patient population.
Administration in locations with different or unpredictable RSV circulation patterns
ACIP recommendations allow for infant RSV antibodies to be administered before October or after March. Tropical climates may have RSV circulation patterns that differ from most of the continental United States or are unpredictable. Locations with tropical climates include but are not limited to southern Florida, Guam, Hawaii, Puerto Rico, US-Affiliated Pacific Islands, and the US Virgin Islands. In Alaska, RSV circulation patterns are less predictable, and the duration of RSV season is often longer than the national average. Public health authorities or regional medical centers may elect to provide revised clinical and public health guidance regarding the ideal timing of infant RSV antibody administration based on local epidemiology and feasibility of implementation, including local supply considerations.
Administration using clinical judgement
Healthcare providers may use clinical judgement in determining when to give infant RSV antibodies and may give them outside of October through March. Special circumstances may also need to be considered, such as travel to areas with increased RSV activity or concerns that the infant or child may not return for a visit when infant RSV antibodies should ideally be administered. Healthcare providers can use clinical judgment to adjust the timing of infant RSV antibody administration for individual patients, and do not need to consult with state or territorial healthcare providers.
Flexibilities in the ACIP recommendations on the timing of infant RSV antibody administration should be considered to optimize patient access, including reimbursement of nirsevimab or clesrovimab.
When infant RSV antibodies can be considered for infants born to vaccinated mothers
An infant RSV antibody may be considered for infants born to vaccinated mothers in rare circumstances when, based on the clinical judgment of the healthcare provider, the potential incremental benefit of administration is warranted. These circumstances may include, but are not limited to:
- Infants born to mothers who may not mount an adequate immune response to RSV vaccination (e.g., people with immunocompromising conditions)
- Infants born to mothers who have medical conditions associated with reduced transplacental antibody transfer (e.g., people living with HIV infection)
- Infants who have undergone cardiopulmonary bypass (see nirsevimab FDA package insert or clesrovimab FDA package insert) or extracorporeal membrane oxygenation (ECMO), or exchange transfusion, leading to loss of maternal antibodies
- Infants with substantial increased risk for severe RSV disease (e.g., hemodynamically significant congenital heart disease, intensive care admission with a requirement of oxygen at discharge)
Dosage
Nirsevimab
- Age less than 8 months
- 50 mg for infants weighing <5 kg [<11 lb]
- 100 mg for infants weighing ≥5 kg [≥11 lb]
- Age 8 months through 19 months:
- 200 mg, administered as two 100-mg injections
Clesrovimab
- 105 mg for all eligible infants
Coadministration with vaccines
Data are limited on administering nirsevimab or clesrovimab with other childhood vaccines. However, neither product is expected to interfere with the immune response to vaccine products.
Infant RSV antibodies and routine childhood vaccines can be administered during the same visit. No interval between infant RSV antibodies and live vaccines (such as measles, mumps, and rubella [MMR] and varicella) is necessary.
Effectiveness
Nirsevimab
Early real-world data show that nirsevimab was at least 70% effective in preventing babies from being hospitalized with RSV.
In clinical studies among infants who were born during or entering their first RSV season, efficacy was evaluated through 150 days after injection. Pooled efficacy from Phase II and III clinical trials in preventing medically attended RSV-associated lower respiratory tract infection (LRTI) was 79.0% and efficacy in preventing RSV-associated LRTI with hospitalization was 80.6%.
Clesrovimab
In clinical studies among infants who were born during or entering their first RSV season, efficacy for preventing medically attended RSV-associated LRTI was 60.4%, and efficacy for preventing RSV-associated LRTI with hospitalization was 90.9% through 150 days after injection.
Safety
Contraindications
Nirsevimab and clesrovimab are contraindicated in infants and children with a history of severe allergic reactions (e.g., anaphylaxis) to any components or excipients in the product. See nirsevimab FDA package insert and clesrovimab FDA package insert.
Precautions
In accordance with CDC's General Best Practice Guidelines for Immunization, children who have a moderate or severe acute illness should usually wait until they recover before getting an infant RSV antibody.
Reporting adverse events
Adverse events might occur after administration of nirsevimab or clesrovimab alone; these reactions may be reported to MedWatch online, by fax, by mail, or by contacting FDA at 1-800-FDA-1088.
Adverse events might occur after the coadministration of infant RSV antibody with a vaccine; these reactions should be reported to the Vaccine Adverse Event Reporting System (VAERS), and reports should specify that the patient received nirsevimab or clesrovimab on the VAERS form in Section 9: "Prescriptions, over-the-counter medications, dietary supplements, or herbal remedies being taken at the time of vaccination." Reports can be submitted to VAERS online, by fax, or by mail. Additional information about VAERS is available by telephone (1-800-822-7967) or online. When adverse events that occur after the coadministration of infant RSV antibodies with a vaccine are reported to VAERS, additional reporting of the same adverse events to MedWatch is not necessary.
To learn more about RSV vaccine safety, go to the following page:
