Respiratory Syncytial Virus, or RSV, is a common virus that infects the lungs and breathing passages. While most people experience mild, cold-like symptoms, the infection can become serious for infants and older adults. For decades, the development of a safe and effective immunization against RSV proved challenging, but recent scientific progress has led to the approval of several new options to protect vulnerable populations from severe disease.
Available RSV Immunizations
The Food and Drug Administration (FDA) has approved three different vaccines for adults to prevent lower respiratory tract disease caused by RSV. Two of these, Arexvy and Abrysvo, are protein-based vaccines, while the third, mRESVIA, uses mRNA technology. All three work by introducing a stabilized version of the RSV fusion (F) protein to the immune system, prompting the body to build a defense against the virus. These vaccines are approved for adults 60 years and older, with some approvals extending to adults as young as 50 who have certain risk factors.
One of the adult vaccines, Abrysvo, also has a specific approval for use in pregnant individuals. When given between 32 and 36 weeks of gestation, the vaccine prompts the pregnant person to create antibodies that are then transferred to the fetus. This process provides protection to the infant from birth through their first six months of life.
For infants and some high-risk young children, a different type of immunization is available called nirsevimab, sold under the brand name Beyfortus. This is not a vaccine but a monoclonal antibody treatment. Instead of stimulating the baby’s own immune system to make antibodies, it provides a direct dose of laboratory-made antibodies that can neutralize the RSV virus.
Efficacy of the Vaccines
For older adults, the Arexvy vaccine was approximately 83% effective in preventing RSV-associated hospitalizations and 77% effective against related emergency department visits during its first season. Protection has been observed to extend over a second RSV season, though specific efficacy rates for the longer term are still being evaluated.
Real-world data from the 2023-2024 RSV season showed the Abrysvo vaccine was about 73% effective at preventing hospitalizations and 79% effective against emergency department visits in those 60 and older. When given during pregnancy, Abrysvo was effective at protecting infants, reducing the risk of severe lower respiratory tract disease by over 80% in their first six months.
The monoclonal antibody, Beyfortus, provides direct and immediate protection for infants. Studies have shown it is effective at preventing hospitalizations and healthcare visits from RSV. This approach is useful for newborns whose immune systems are not yet fully developed, as the direct infusion of antibodies provides temporary defense.
Safety and Side Effects
Most side effects from RSV immunizations are mild and temporary. For the adult vaccines Arexvy, Abrysvo, and mRESVIA, the most common reactions include pain, redness, or swelling at the injection site. Other side effects are fatigue, headache, muscle pain, and joint stiffness, which typically resolve within a day or two.
For infants receiving the Beyfortus monoclonal antibody, the most common side effects are also mild, consisting primarily of rash and injection site reactions. These events are generally not serious and resolve on their own. Clinical trials showed the antibody was well-tolerated by infants and young children.
Public health agencies continue to monitor for any rare adverse events. For the adult vaccines, there have been isolated reports of inflammatory neurologic conditions, such as Guillain-Barré syndrome (GBS), and instances of atrial fibrillation. Regulatory bodies have noted these events are infrequent, and ongoing surveillance is in place to better understand any potential association.
Official Recommendations
The Centers for Disease Control and Prevention (CDC) recommends a single dose of an RSV vaccine for all adults ages 75 and older. For those aged 60 to 74, the recommendation is based on shared clinical decision-making, where individuals discuss their personal risk factors with a healthcare provider to determine if vaccination is appropriate.
For pregnant individuals, the CDC recommends a single dose of the Abrysvo vaccine between 32 and 36 weeks of gestation, timed to maximize antibody transfer to the baby before birth. This is a seasonal recommendation, intended to protect infants born just before and during the RSV season.
The CDC also recommends one dose of Beyfortus for all infants who are younger than 8 months and entering their first RSV season. A dose is also recommended for a small group of children between 8 and 19 months old who are at increased risk for severe RSV disease, such as those with chronic lung disease or who are severely immunocompromised.