Respiratory Syncytial Virus (RSV) is a widespread respiratory virus that typically causes mild, cold-like symptoms. However, it can lead to severe lung infections, such as bronchiolitis and pneumonia, particularly in certain vulnerable populations.
Distinguishing Live and Non-Live Vaccines
Live-attenuated vaccines contain a weakened form of the living virus or bacteria. This weakened pathogen can still replicate in the body, mimicking a natural infection without causing severe illness. This typically elicits a strong, long-lasting immune response, often providing protection with one or two doses.
Non-live vaccines, in contrast, do not contain any live components of the pathogen. These include inactivated vaccines, which use killed versions of the germ, or subunit vaccines, which contain only specific pieces of the pathogen, such as proteins or sugars. These vaccines stimulate an immune response without causing the disease. However, they may require multiple doses or booster shots to maintain robust protection, as the immune response may not be as strong or long-lasting as that from live-attenuated vaccines.
Current RSV Prevention Strategies
Currently available RSV vaccines, such as Arexvy and Abrysvo, are not live vaccines; they are subunit vaccines. These vaccines specifically target the prefusion form of the RSV fusion (F) protein. By introducing this protein, the vaccines stimulate the immune system to produce antibodies that can neutralize the virus. Arexvy contains a recombinant RSV F protein antigen from the RSV-A subtype and includes an adjuvant to enhance the immune response. Abrysvo is a bivalent recombinant protein vaccine, containing prefusion F antigens from both RSV-A and RSV-B subtypes.
Beyond vaccines, Nirsevimab (marketed as Beyfortus) offers another prevention strategy and is a monoclonal antibody product, not a vaccine in the traditional sense. This product provides passive immunity by directly supplying pre-formed antibodies to the body. Nirsevimab binds to a conserved site on the RSV F protein, preventing the virus from fusing with host cells. This long-acting monoclonal antibody is designed to offer protection for an entire RSV season with a single dose.
Target Populations for RSV Prevention
RSV prevention strategies protect specific populations at higher risk of severe disease. Older adults, particularly those aged 60 and above, are a target group for RSV vaccination, with Arexvy and Abrysvo approved. These vaccines help to prevent lower respiratory tract disease caused by RSV in this age group, who often have weakened immune systems or underlying health conditions.
Pregnant individuals are another target for RSV prevention, with Abrysvo approved for maternal vaccination. When administered between 32 and 36 weeks of gestation, the antibodies produced by the pregnant person are transferred across the placenta to the developing baby. This transfer provides passive immunity, protecting infants from severe RSV infection from birth through their first six months of life.
Infants and young children are also vulnerable to severe RSV disease. Nirsevimab is recommended for infants younger than 8 months entering their first RSV season. It is also recommended for children aged 8 months to 19 months who have increased risk for severe RSV during their second RSV season. This monoclonal antibody provides immediate protection, especially beneficial for newborns and those whose mothers did not receive the RSV vaccine during pregnancy.