Respiratory Syncytial Virus, or RSV, is a common virus that causes mild, cold-like symptoms in most healthy individuals. However, the virus can lead to severe respiratory illness, particularly for infants and older adults, who are more susceptible to complications like pneumonia and bronchiolitis. After decades of research, the U.S. Food and Drug Administration (FDA) has approved the first immunizations designed to protect these vulnerable populations from severe outcomes associated with RSV.
Vaccines Approved for Older Adults
The FDA has approved two vaccines to protect adults aged 60 and older from severe RSV infections: GSK’s Arexvy and Pfizer’s Abrysvo. Both are designed to prevent lower respiratory tract disease (LRTD) by introducing a stabilized form of the RSV fusion (F) protein to the body. This protein is what the virus uses to enter human cells.
Presenting this protein to the immune system triggers the production of protective antibodies without causing illness. This response prepares the body to recognize and fight off the actual virus upon future exposure. The availability of these vaccines offers a direct method for older individuals to bolster their immunity against a virus that previously had no vaccine-based prevention.
Protective Measures for Infants
Protecting infants from RSV involves two distinct strategies approved by the FDA. One approach is maternal vaccination using Pfizer’s Abrysvo, which is approved for administration to individuals during weeks 32 through 36 of pregnancy. The pregnant person generates antibodies against the RSV F protein, which are then transferred to the fetus through the placenta. This provides the newborn with passive immunity that helps protect them from birth through their first six months of life.
A different method of protection comes from a monoclonal antibody product called nirsevimab, sold as Beyfortus. Beyfortus is not a vaccine; it does not stimulate the infant’s own immune system to create a lasting response. Instead, it provides passive immunity by delivering a laboratory-developed antibody directly to the infant via injection. This single dose offers immediate protection against RSV-LRTD for the duration of the RSV season and is recommended for infants born during or entering their first season.
Assessed Efficacy and Safety Profiles
The FDA’s approval of these products was based on extensive clinical trial data. For older adults, GSK’s Arexvy demonstrated an efficacy of 94.6% in preventing RSV-associated lower respiratory tract disease in one study. Pfizer’s Abrysvo showed an efficacy of 66.7% against the same condition in its primary clinical trial for older adults during the first season post-vaccination. For infants, maternal immunization with Abrysvo was found to reduce the risk of severe LRTD in the first few months after birth, and Beyfortus showed high efficacy in protecting infants from medically attended RSV-related infections.
The safety profiles were also thoroughly evaluated. The most frequently reported side effects for Arexvy and Abrysvo in older adults included:
- Injection site pain
- Fatigue
- Muscle pain
- Headache
For the maternal Abrysvo vaccine, the FDA noted a potential, though not statistically significant, increased risk of preterm birth in clinical trials, a factor included in the product’s informational labeling. For Beyfortus, the most common adverse reactions were rash and injection site reactions. These side effects were mild and temporary.
Federal Guidance on Administration
Following FDA approval, the Centers for Disease Control and Prevention’s (CDC) Advisory Committee on Immunization Practices (ACIP) provides recommendations on use. For adults 75 and older, the CDC recommends a single dose of an RSV vaccine. For adults aged 60 to 74, the CDC suggests shared clinical decision-making, where individuals discuss their personal health risks with their healthcare provider to determine if vaccination is appropriate.
For expectant parents, the ACIP recommends a single dose of the Abrysvo vaccine between 32 and 36 weeks of gestation to protect the newborn. For direct infant protection, the CDC recommends that all infants under 8 months of age receive a dose of nirsevimab (Beyfortus) shortly before or during their first RSV season. These guidelines help healthcare providers understand who is eligible for these new preventative measures and the optimal timing for administration.