Respiratory Syncytial Virus (RSV) is a common respiratory illness that typically causes mild, cold-like symptoms in most individuals. However, for certain populations, such as infants and older adults, RSV infection can lead to more severe outcomes, including serious lower respiratory tract disease and hospitalization. New preventative treatments, including vaccines and monoclonal antibody products, offer protection against this widespread virus.
Common and Mild Side Effects
Individuals receiving RSV vaccines, such as Arexvy and Abrysvo, commonly experience mild and temporary reactions. These include localized responses at the injection site, such as pain, redness, and swelling, which often resolve within a few days.
Beyond the injection site, systemic reactions are also observed. These can include fatigue, headache, and muscle or joint pain. Some individuals might also experience a low-grade fever or nausea. Such general symptoms are usually mild and subside within a few days.
Potential Risks for Pregnant Individuals
The maternal RSV vaccine, Abrysvo, is administered during pregnancy, specifically between 32 and 36 weeks of gestation, to protect the newborn. Clinical trials noted a numerical difference in preterm births: 5.7% in vaccinated mothers compared to 4.7% in the placebo group.
Regulatory bodies like the FDA carefully evaluated this data. While a numerical difference was observed, the available information was considered insufficient to definitively establish or rule out a causal relationship between the vaccine and preterm birth. The FDA has since required post-marketing studies to continue monitoring this potential signal, and to assess for hypertensive disorders of pregnancy, including pre-eclampsia, which occurred in 1.8% of Abrysvo recipients compared to 1.4% in the placebo group.
Potential Risks for Older Adults
For individuals aged 60 and older, for whom the RSV vaccines Arexvy and Abrysvo are approved, rare but serious risks have been identified. The most notable is Guillain-Barré Syndrome (GBS). GBS is a rare condition where the body’s immune system attacks its nerves, potentially leading to muscle weakness, tingling, and paralysis.
A small number of GBS cases were reported in clinical trials and post-market surveillance following vaccination. The estimated risk for GBS associated with these vaccines is very small, with studies suggesting approximately 10 excess cases per 1 million vaccinated adults aged 60 or older. A US observational study found about nine excess cases per million Abrysvo doses and seven excess cases per million Arexvy doses in adults 65 and above.
Concerns Related to Infant Antibody Treatments
The preventative shot for infants, nirsevimab (marketed as Beyfortus), operates differently from a traditional vaccine. It is a monoclonal antibody, which means it provides passive immunity by directly introducing protective proteins into the infant’s body. This antibody is designed to attach to the RSV F protein, preventing the virus from entering the body’s cells, particularly those in the lungs.
The safety profile for this monoclonal antibody treatment is generally characterized by mild side effects. The most commonly reported reactions include rash, which may appear within 14 days after injection, and local injection site reactions such as pain, swelling, or redness, often occurring within 7 days. A low-grade fever has also been reported in a small percentage of infants. These effects are typically mild to moderate and transient.