Respiratory Syncytial Virus (RSV) is a common seasonal illness that frequently affects the respiratory system, particularly impacting infants and young children. This virus can lead to serious lower respiratory tract infections, such as bronchiolitis and pneumonia, often necessitating hospital care for severe cases. To help protect vulnerable populations from the effects of RSV, a new preventative measure involving monoclonal antibodies has emerged.
What are RSV Monoclonal Antibodies?
Monoclonal antibodies (mAbs) are laboratory-produced proteins that mimic the natural antibodies the human body creates to fight off infections. In the context of RSV, these mAbs are specifically designed to target and bind to a particular protein on the surface of the RSV virus, known as the fusion (F) protein. By attaching to this protein, the antibodies can neutralize the virus, preventing it from entering and infecting healthy cells. This mechanism provides direct, immediate protection against the virus.
This form of protection is known as “passive immunity” because the antibodies are directly given to the individual, rather than the body producing its own immune response. This immunity is immediate, but temporary, lasting only as long as the administered antibodies remain in the body.
This differs from “active immunity,” generated by traditional vaccines. Vaccines stimulate the body’s own immune system to produce antibodies and memory cells. While this process takes several weeks to develop full protection, the resulting immunity can be long-lasting. RSV monoclonal antibodies offer a ready-made defense, whereas traditional vaccines train the body to build its own.
Who Receives RSV Monoclonal Antibodies?
RSV monoclonal antibodies are recommended for infants and young children at increased risk of severe illness. The main target populations include infants born during or entering their first RSV season, generally babies under eight months of age. Some children aged 8 through 19 months at higher risk for severe RSV disease may also receive a dose in their second RSV season.
Administration is typically a single dose given before or early in the RSV season. For example, nirsevimab is given as a single injection. Dosage varies by infant weight: for those under 8 months, 50 mg for infants under 5 kg, and 100 mg for infants 5 kg or more. Older children aged 8 through 19 months receive a 200 mg dose, typically as two separate 100 mg injections. The preferred injection site is the anterolateral thigh region.
Benefits and Safety of RSV Monoclonal Antibodies
RSV monoclonal antibodies offer benefits in preventing severe outcomes. These antibodies have shown high efficacy in significantly reducing the risk of severe RSV lower respiratory tract disease. Studies indicate a notable decrease in RSV-related hospitalizations and emergency department visits. This reduction in severe illness helps improve infant health outcomes.
A single dose of RSV monoclonal antibodies, such as nirsevimab, provides protection for at least five months, covering the entire RSV season. This extended duration means only one administration is needed for seasonal coverage. While antibodies do not provide long-term immunity beyond one season, the risk of severe RSV infection and hospitalization decreases after the first year of life.
RSV monoclonal antibodies are well-tolerated, with common side effects being mild and temporary. These may include local reactions at the injection site, such as pain, redness, or swelling, and sometimes a rash. These reactions are transient and resolve on their own. Clinical trials have demonstrated the overall safety of these monoclonal antibodies, even when administered concurrently with routine childhood vaccines.