As the 2026–2027 respiratory syncytial virus season approaches, parents now have more than one way to protect an infant from severe RSV, but the choices can be confusing. A September 2026 American Academy of Pediatrics policy update keeps the basic first-season strategy intact while expanding the group of high-risk children who should receive protection during a second RSV season.
What to know in 30 seconds
- For most infants entering their first RSV season, protection comes from either maternal RSV vaccination during pregnancy or a long-acting RSV antibody given to the infant.
- Nirsevimab and clesrovimab are both options for eligible infants younger than 8 months in their first season, but only nirsevimab is used for high-risk children entering a second season.
- The AAP broadened its 2026 second-season high-risk criteria to include additional children with extreme prematurity, significant heart disease, certain pulmonary or neuromuscular disorders, and some chromosomal conditions.
RSV prevention for infants now has three main routes
RSV remains one of the most important causes of lower respiratory tract disease in early infancy. The prevention strategy in the United States now uses two different biological approaches: vaccination during pregnancy so antibodies cross the placenta before birth, or direct administration of a long-acting monoclonal antibody to the infant.
The maternal option is Pfizer’s RSVpreF vaccine, Abrysvo, given during weeks 32 through 36 of pregnancy during the recommended seasonal window. The infant options are nirsevimab (Beyfortus) and clesrovimab (Enflonsia). These monoclonal antibodies do not train the infant’s immune system the way a vaccine does. They provide ready-made antibodies that can neutralize RSV soon after administration.
For most infants, the goal is one route of protection rather than both. Infants younger than 8 months who are born during or entering their first RSV season should receive an infant antibody if the pregnant parent did not receive the maternal RSV vaccine, vaccination status is unknown, or the infant was born less than 14 days after maternal vaccination. Our earlier explainer on nirsevimab versus maternal RSV vaccination breaks down how those two strategies differ.
Nirsevimab and clesrovimab are both first-season options
For an eligible infant in the first RSV season, the AAP does not prefer nirsevimab over clesrovimab. Both are long-acting monoclonal antibodies designed to cover the months when severe RSV risk is highest.
The dosing is different. Nirsevimab is weight-based in the first season: 50 mg for infants weighing less than 5 kg and 100 mg for infants weighing at least 5 kg. Clesrovimab is given as a fixed 105 mg dose regardless of weight. A separate Bites of Bio comparison explains the practical differences between nirsevimab and clesrovimab.
Timing matters almost as much as product choice. In most of the continental United States, RSV antibody administration is concentrated from October through March. Babies born during the season should ideally receive protection within the first week of life, often during the birth hospitalization. Infants born before the season can receive an antibody shortly before RSV activity rises.
Real-world data show substantial protection against hospitalization
By 2026, the evidence base had moved beyond the original registration trials. A CDC-led study published in Pediatrics analyzed electronic health record data from five U.S. health systems during the 2024–2025 RSV season.
Among 3,531 emergency department encounters and 470 hospitalizations included in the nirsevimab analysis, estimated effectiveness was 62% against RSV-associated emergency department encounters and 77% against RSV-associated hospitalization. In the maternal RSV vaccine analysis, effectiveness was 49% against emergency department encounters and 82% against hospitalization.
Those are observational effectiveness estimates rather than randomized-trial efficacy estimates, so they should not be compared as if they came from a head-to-head trial. The study used separate test-negative analyses for the two prevention strategies, and confidence intervals were wider for the maternal vaccine because fewer encounters were available.
The broader message is still important: both approaches were associated with meaningful protection against severe RSV outcomes in routine U.S. practice. For nirsevimab specifically, protection is designed to cover roughly one RSV season. We reviewed the duration data in more detail in how long nirsevimab protects infants from RSV.
The 2026 AAP update expands second-season eligibility
The biggest change for the 2026–2027 season is not in healthy young infants. It is in children 8 through 19 months of age who remain at unusually high risk as they enter a second RSV season.
The AAP continues to include children with chronic lung disease of prematurity requiring recent medical support, severe immunocompromise, certain severe cystic fibrosis manifestations, and American Indian or Alaska Native children. Its September 2026 policy adds four broader risk groups:
- children born before 32 weeks of gestation, even if they no longer require medication or respiratory support;
- children with hemodynamically significant congenital heart disease;
- children with anatomic pulmonary abnormalities or neuromuscular disorders that increase the risk of severe RSV disease;
- children with Down syndrome or other chromosomal differences associated with increased risk of severe RSV disease.
For children who qualify for protection in a second RSV season, nirsevimab is the recommended antibody. Clesrovimab is not approved for children entering their second RSV season. The recommended nirsevimab dose for eligible children 8 through 19 months is 200 mg, given as two 100 mg intramuscular injections. Our Beyfortus dosing guide explains the first- and second-season dosing structure.
AAP and CDC guidance are not identical yet
There is an important 2026 nuance for clinicians and families reading different websites. The AAP’s September 2026 policy expanded the second-season high-risk list, while the CDC infant RSV guidance available at the time of this article still lists the earlier, narrower set of second-season groups.
That does not change the first-season recommendation: both organizations support protecting eligible infants through maternal vaccination or a long-acting infant antibody. But for a child entering a second season because of prematurity, congenital heart disease, neuromuscular disease, pulmonary abnormalities, or a chromosomal condition, clinicians may need to reconcile the newer AAP guidance with current payer policies and local implementation.
The AAP has said it is working with insurers to support coverage for the expanded indications. Access can also depend on whether birthing hospitals stock the products and whether they participate in the Vaccines for Children program.
Why most healthy toddlers do not need another RSV antibody
RSV risk is not constant across childhood. Hospitalization risk is highest in the first months of life and falls substantially with age. That is why second-season immunization is targeted rather than universal.
A healthy child who is 8 months or older and does not meet a high-risk criterion generally does not receive another RSV antibody simply because a new RSV season has started. The second-season strategy is intended for children whose underlying conditions keep their risk of severe disease unusually high.
What parents should ask before RSV season starts
For a newborn or young infant, the most useful question is whether protection already came through maternal RSV vaccination. If not, the next question is whether the infant should receive nirsevimab or clesrovimab and when the dose should be given.
For a child entering a second RSV season, the key issue is whether the child falls into one of the high-risk groups. Because the AAP expanded that list in 2026, families of children born very prematurely or living with significant cardiac, pulmonary, neuromuscular, immune, cystic fibrosis, or chromosomal conditions should review eligibility with the child’s clinician before RSV activity rises.
What the evidence still cannot answer
Current guidance is supported by randomized trials, post-authorization surveillance, and real-world effectiveness studies, but several uncertainties remain. Effectiveness estimates vary by season, viral circulation, time since immunization, population, and study design. Clesrovimab has less real-world experience than nirsevimab because it entered routine use later.
There is also no randomized head-to-head trial showing that one of the two infant monoclonal antibodies is clinically superior to the other. Likewise, observational estimates for maternal vaccination and infant antibody administration should not be used to declare one strategy better for every family. Timing of birth, maternal vaccination status, product availability, medical risk, and parent preference all matter.
References
- American Academy of Pediatrics Committee on Infectious Diseases. Recommendations for the Prevention of Respiratory Syncytial Virus Disease in Infants and Children: Policy Statement. Pediatrics. 2026. DOI: 10.1542/peds.2026-079047.
- Payne AB, et al. Effectiveness of RSV Prevention Strategies in US Infants: 2024–2025. Pediatrics. 2026;158(3):e2026076089. DOI: 10.1542/peds.2026-076089.
- Centers for Disease Control and Prevention. RSV Immunization Guidance for Infants and Young Children. 2026. CDC clinical guidance.