Introduction
Respiratory syncytial virus (RSV) remains one of the most common and dangerous respiratory infections in early infancy. Nearly every child encounters RSV by the age of two, but for newborns and young babies, especially those under six months, the infection can cause severe bronchiolitis or pneumonia and lead to hospitalization. Each RSV season, which typically spans from October through March in most of the United States, places substantial pressure on pediatric hospitals.
Until recently, preventing RSV in the youngest infants was challenging. Palivizumab, the only available antibody for years, required monthly injections and was reserved for high-risk babies. That changed in 2023–2024, when two new, broader preventive strategies were approved: maternal vaccination during late pregnancy (Pfizer’s Abrysvo, or RSVpreF) and long-acting monoclonal antibodies for infants (nirsevimab, marketed as Beyfortus, and the newer clesrovimab expected for wider use in 2025–2026).
Both approaches have proven highly effective in preventing severe RSV disease. However, because they target different stages (before or after birth), families must understand how timing, local RSV circulation, and clinical recommendations influence the best choice.
This article outlines how these new tools work, when they should be administered, how long protection lasts, and how parents, obstetricians, and pediatricians can coordinate care ahead of the 2025–2026 RSV season.
RSV in Infancy: Why Protection Matters
Respiratory syncytial virus is a leading cause of lower respiratory tract infections among infants in the United States. Each year, between 58,000 and 80,000 children under five are hospitalized with RSV, and the majority of these admissions occur in babies younger than six months. The virus spreads easily through respiratory droplets and contaminated surfaces, thriving during the cooler months, typically October through March in most regions, though the season can start earlier in the South and last longer in Alaska.
For most older children and adults, RSV resembles a common cold. In infants, however, it can rapidly progress to bronchiolitis or pneumonia, causing difficulty breathing, dehydration, and in severe cases, the need for intensive care. The youngest babies, especially those born prematurely or with chronic heart or lung conditions, are at the greatest risk. Infants exposed to secondhand smoke, attending daycare, or living with school-age siblings are also more likely to contract RSV early and experience severe symptoms.
Since the immune system of newborns is still immature, these infants are unable to produce strong or lasting immune responses to infection or vaccination. Active RSV vaccines for babies are still in development, leaving passive protection as the main strategy. This means supplying antibodies from an external source either through the mother’s immune system during pregnancy or directly into the baby’s bloodstream after birth.
Before 2023, the only preventive option was palivizumab (Synagis), a monoclonal antibody given monthly to high-risk infants. While effective, its high cost and complex dosing limited use to a small group of patients. The new generation of preventive tools, namely, maternal RSV vaccination and long-acting antibodies such as nirsevimab and clesrovimab, has fundamentally changed the landscape. They allow protection for nearly all infants, often with a single dose timed to coincide with the start of the RSV season.
As the virus continues to cause yearly surges in hospitalizations, these advances represent one of the most important steps in pediatric infectious disease prevention in decades.
Maternal RSV Vaccine (Abrysvo): Timing, Efficacy, and Access
The maternal RSV vaccine, known by its brand name Abrysvo and developed by Pfizer, marked a turning point in infant respiratory protection when it was licensed by the FDA and recommended by the CDC in 2023. Unlike pediatric immunizations, which stimulate the infant’s own immune response, Abrysvo is administered to the pregnant person. The vaccine trains the maternal immune system to produce antibodies against RSV, which are then transferred through the placenta to the fetus during the final weeks of pregnancy. These antibodies circulate in the newborn’s bloodstream, providing immediate passive protection from the moment of birth.
The CDC recommends giving the vaccine between 32 and 36 weeks of gestation, specifically, between 32 0/7 and 36 6/7 weeks. This window is optimal for maximizing antibody transfer while avoiding delivery before immunity is established. Since RSV follows a seasonal pattern, the vaccine is offered to eligible pregnant people during the months when RSV typically circulates: September through January in most of the continental United States. States such as Florida or Alaska may adjust these dates to reflect earlier or prolonged viral activity.
Clinical trials demonstrated that maternal vaccination with Abrysvo reduced the risk of severe RSV-associated lower respiratory tract disease in infants by more than 80% during the first three months of life and continued to offer significant protection through six months of age. The vaccine’s single-dose schedule makes it simple to integrate into routine prenatal care alongside influenza and Tdap vaccination. Safety monitoring from both trials and early real-world data has shown the vaccine to be well tolerated. The most common reactions are mild injection-site pain and fatigue. Some analyses raised the possibility of a slightly higher rate of preterm birth among vaccine recipients, but no causal link has been confirmed, and major medical organizations, including the American College of Obstetricians and Gynecologists (ACOG) and the Society for Maternal-Fetal Medicine (SMFM), strongly endorse its use based on the overwhelming evidence of benefit.
Timing remains crucial. If a baby is born fewer than 14 days after vaccination, there may not be enough time for sufficient antibody transfer, and the newborn may still be recommended to receive monoclonal antibody protection (such as nirsevimab). For infants born more than two weeks after maternal vaccination, antibody levels are typically high enough to provide coverage for the entire RSV season.
Abrysvo is covered by most commercial insurers, Medicaid, and the Vaccines for Children (VFC) program in states that include maternal immunizations. Many obstetric practices and retail pharmacies now stock it, allowing vaccination during a routine prenatal visit or through pharmacy referral.
By including RSV vaccination as part of standard pregnancy care, healthcare providers can ensure that newborns begin life with a strong layer of protection well before they take their first breath.
Infant Antibodies (Nirsevimab / Clesrovimab): What Families Should Know
For infants who are not protected through maternal vaccination or when maternal vaccination occurs too close to delivery, monoclonal antibodies provide a powerful alternative defense. These products do not function like vaccines; instead of teaching the immune system to recognize the virus, they deliver ready-made antibodies that circulate in the infant’s bloodstream for several months, blocking RSV from infecting the lungs. The two main antibody options for the 2025–2026 season are nirsevimab and clesrovimab, both designed to offer broad, long-lasting protection with a single injection.
Nirsevimab (Beyfortus) was approved by the FDA in 2023 and rapidly adopted by the CDC and the American Academy of Pediatrics (AAP). It is recommended for all infants younger than eight months who are entering or born during their first RSV season, typically October through March. The dose is based on weight: 50 mg for infants under 5 kg (11 lb) and 100 mg for those 5 kg and above. A single intramuscular injection provides protection for about five months, long enough to cover an entire RSV season. The clinical data behind nirsevimab are striking. In pivotal trials, the antibody reduced RSV-related hospitalizations by nearly 80% and emergency department visits by more than 75%. Real-world studies during the first U.S. rollout confirmed those findings, showing that infants who received nirsevimab were substantially less likely to require hospitalization or supplemental oxygen. Side effects have been minimal, limited mainly to mild soreness at the injection site or low-grade fever.
The newer Clesrovimab (Enflonsia), expected to gain broader use in 2025–2026, works in a similar way but has an even longer half-life, potentially extending protection beyond six months. Early international trials have demonstrated efficacy comparable to nirsevimab, with a similarly favorable safety profile. While full U.S. availability may vary during the first year of introduction, experts expect clesrovimab to become a key option for pediatric practices and hospital newborn units once distribution expands.
Timing of administration is most important. Infants born during the RSV season should receive antibody protection within the first week of life, ideally before hospital discharge. Those born before the season starts should get the injection just before RSV activity increases, usually in early October. For high-risk children aged 8–19 months, such as those with chronic lung disease, immunocompromise, or certain congenital conditions, nirsevimab may be repeated before their second RSV season. Clesrovimab’s role for older infants will be determined as additional data accumulate.
One of the key advantages of these antibodies is that they can protect babies regardless of whether the mother was vaccinated during pregnancy. However, if the maternal RSV vaccine was given at least 14 days before delivery, the infant is considered already protected and does not require antibody administration. If vaccination occurred later or did not occur at all, nirsevimab or clesrovimab should be used.
In practice, families will typically receive antibody protection in the birth hospital or during the first pediatric visit. Access and insurance coverage have improved since the 2023–2024 rollout, when nirsevimab demand briefly outpaced supply. For the 2025–2026 season, the CDC and manufacturers expect sufficient stock through both private insurance and the Vaccines for Children (VFC) program, ensuring equitable access across states.
Monoclonal antibodies such as nirsevimab and clesrovimab give pediatricians and parents an effective, once-per-season solution to prevent severe RSV infection. As these products become standard practice, they promise to dramatically reduce winter hospitalizations and help infants through their most vulnerable months with fewer risks and fewer hospital stays.
Making the Right Choice: Family Scenarios and Clinical Guidance
Both the maternal RSV vaccine and infant antibody immunization offer excellent protection, but in most cases, only one is needed. The best option depends primarily on timing: when the pregnant person is vaccinated, when the baby is born, and where in the country the family lives.
If maternal vaccination occurs between 32 and 36 weeks of pregnancy and at least two weeks before delivery, the newborn receives antibodies through the placenta and is considered protected. No further injection is necessary unless the infant has special medical conditions that justify additional protection. This approach works particularly well for pregnancies that overlap with the start of RSV season, ensuring that the baby is covered immediately after birth. If the maternal vaccine was not received, or if the birth occurred less than two weeks after vaccination, monoclonal antibody protection is the next line of defense. Nirsevimab or clesrovimab should be administered within the first week of life for babies born during RSV season—or just before the season begins for those born in summer. Families living in areas with early or extended RSV activity, such as southern states or Alaska, should follow regional guidance for scheduling.
In a small number of cases, clinicians may recommend both maternal vaccination and antibody administration, for example, if the infant is severely premature or medically fragile. However, this is the exception rather than the rule.
For parents, the key is to plan early. Discuss RSV prevention during prenatal visits and confirm the timing of vaccination with the obstetric team. After delivery, ensure that the pediatrician knows the maternal vaccine status so antibody administration can be scheduled appropriately. Pharmacies, birthing hospitals, and clinics now collaborate to provide both options, simplifying access for families.
When properly timed and coordinated, these preventive tools give every baby a strong, science-backed start to their first RSV season.
Conclusion
The arrival of new RSV prevention options marks a major step forward in protecting infants from one of the most common causes of early hospitalization. For the first time, families and clinicians can choose between two proven, one-time interventions – maternal vaccination or infant antibody immunization – both of which dramatically reduce the risk of severe respiratory illness during a baby’s first winter.
For many parents, the decision will depend simply on timing. If the pregnant person receives the RSV vaccine between 32 and 36 weeks of gestation at least two weeks before delivery, the newborn will be well protected from birth. If vaccination was missed or occurred too close to labor, the baby can still receive direct protection through nirsevimab or clesrovimab after delivery. In both cases, the protection lasts through the peak RSV months and fades naturally as the infant’s immune system matures. These advances also reflect a broader shift in pediatric prevention from treating infection to anticipating it. By coordinating between obstetric and pediatric care, discussing RSV prevention during routine visits, and planning ahead for seasonal timing, families can help ensure that their newborns begin life shielded against one of the most serious respiratory threats of early infancy.
As the 2025–2026 season approaches, the message from public health experts is clear: RSV prevention now fits easily into the standard care pathway. A single well-timed step before or just after birth can protect the most vulnerable babies from the dangers of their first winter.