Respiratory Syncytial Virus (RSV) is a common respiratory infection that typically causes mild, cold-like symptoms in older children and adults. However, it poses a significant threat to newborns and young infants, often peaking during the fall and winter. RSV is a leading cause of hospitalization for babies under six months of age, even among those with no underlying health conditions. The virus can cause severe lung infections such as bronchiolitis and pneumonia. Protecting a newborn involves environmental controls, utilizing maternal immunity, and, when necessary, direct antibody prophylaxis.
Non-Medical Steps for Environmental Control
Consistent hygiene and exposure management are the first line of defense against RSV. Strict enforcement of hand hygiene is essential for anyone interacting with the newborn. Caregivers and visitors should wash their hands with soap and water for at least 20 seconds before touching the baby.
Limiting the newborn’s exposure to sick individuals is highly effective, even if the illness seems like a mild cold. RSV is easily transmitted through airborne droplets and can live on hard surfaces for several hours. Postpone visits from anyone showing cold-like symptoms and minimize the baby’s time in crowded public spaces.
Parents should regularly clean and disinfect high-touch surfaces in the home, including doorknobs, countertops, toys, and crib rails. Eliminating all tobacco smoke exposure is also an important preventative measure. Exposure to secondhand smoke significantly increases a newborn’s risk for severe RSV disease.
Protecting the Newborn Through Maternal Immunity
Protecting newborns involves leveraging the mother’s immune system during pregnancy to pass protective antibodies to the fetus. This is achieved using a specific vaccine, such as Abrysvo, administered to the mother to stimulate antibody production against RSV. These antibodies cross the placenta, entering the baby’s bloodstream in a process known as passive immunity.
The recommended timing for maternal vaccination is during weeks 32 through 36 of pregnancy, ideally during the RSV season (September through January). Studies suggest that vaccination earlier in this window, around 32 weeks, may maximize the transfer of antibodies. This ensures the infant has a high level of protection throughout the first six months of life, the period of highest risk for severe RSV.
Clinical trials have demonstrated the effectiveness of this maternal strategy in preventing severe illness in infants. The vaccine has been shown to reduce the risk of a baby being hospitalized due to RSV by 57%. It also reduces the risk of a healthcare visit for RSV by 51% within six months after birth.
Antibody Prophylaxis for Direct Infant Protection
For infants, passive immunity involves administering pre-made antibodies directly to the baby, known as antibody prophylaxis. This provides immediate, temporary defense against the Respiratory Syncytial Virus without requiring the baby’s own immune system to generate a response. The newest and most broadly recommended option is a long-acting monoclonal antibody called nirsevimab (Beyfortus), designed to provide protection for an entire RSV season.
Nirsevimab is recommended for all infants under eight months of age who are entering or are born during their first RSV season. This single intramuscular injection is ideally given shortly before the season begins. For babies born during the season, it can be given within the first week of life, sometimes even before hospital discharge. The antibody is engineered with a modification that significantly extends its half-life, allowing one dose to confer protection for at least five months.
The dosing of nirsevimab is weight-based for infants under eight months. Those weighing less than 5 kilograms receive a 50 mg dose, while those 5 kilograms or more receive a 100 mg dose. In rare cases, the antibody is also recommended for high-risk children aged 8 to 19 months entering their second RSV season. This universal recommendation addresses the fact that most infants hospitalized for RSV are otherwise healthy, making broad protection necessary.
A different, older monoclonal antibody, palivizumab (Synagis), is also available but is now typically reserved for a very specific, high-risk group of infants. Palivizumab has a much shorter half-life and requires monthly injections throughout the five-month RSV season. This option is generally reserved for infants with underlying conditions like prematurity, certain chronic lung diseases, or specific congenital heart conditions.
Parents must consult with their pediatrician to determine the most appropriate strategy for their baby’s protection. Infants whose mothers received the maternal RSV vaccine at least 14 days before birth are generally not recommended to receive nirsevimab, as the protection has already been successfully passed to the baby. The choice between maternal vaccination and direct infant prophylaxis is a shared decision, as both are highly effective tools for preventing severe RSV disease.