Respiratory Syncytial Virus (RSV) is a widespread respiratory virus that commonly causes mild, cold-like symptoms. However, it can lead to more serious conditions, such as bronchiolitis and pneumonia, particularly in vulnerable groups like infants, young children, and older adults. Understanding how the body develops immunity to RSV, whether through natural infection or medical interventions, is important for protecting these populations.
Natural Immunity Following RSV Infection
When an individual contracts RSV, their body produces antibodies. These antibodies offer some protection, but immunity from natural infection is often incomplete and short-lived. This means individuals can experience repeat RSV infections throughout their lives.
Subsequent infections are typically milder, but can still cause severe illness, especially in those with underlying health conditions or weakened immune systems. This characteristic makes RSV a recurrent illness, differing from viruses that confer lifelong immunity after a single infection.
Passive Immunity and Protection for Infants
Passive immunity provides immediate, temporary protection against RSV by directly introducing antibodies into the body, rather than stimulating the body to produce its own. This approach is particularly beneficial for infants, who are highly vulnerable to severe RSV disease. Infants acquire passive immunity through maternal antibodies, transferred from the mother during pregnancy, primarily in the third trimester. These antibodies offer protection for approximately six months after birth, though their levels decline over time.
Another method of passive immunity involves monoclonal antibody products like nirsevimab (Beyfortus) and palivizumab (Synagis). Nirsevimab is a single-dose, long-acting antibody that targets the RSV fusion (F) protein, preventing the virus from entering cells. It provides protection for at least five months, potentially covering an entire RSV season for infants. Palivizumab, another monoclonal antibody, also binds to the RSV F protein to prevent infection and is administered monthly during the RSV season to high-risk infants and young children, such as those born prematurely or with certain heart or lung conditions. Nirsevimab offers a longer half-life compared to palivizumab, allowing for single-dose administration for season-long protection.
Active Immunity Through Vaccination
Active immunity against RSV is stimulated by vaccines, prompting the body to produce its own protective antibodies. Recently approved RSV vaccines offer new strategies for protection, particularly for older adults and infants. For older adults aged 60 and above, vaccines like Abrysvo (Pfizer) and Arexvy (GSK) are available. These vaccines contain a stabilized form of the RSV fusion (F) protein.
Upon administration, these vaccines stimulate the immune system to recognize and fight RSV, reducing the risk of lower respiratory tract disease. Both Arexvy and Abrysvo are approved for adults 60 years and older, and are given as a single intramuscular dose.
Abrysvo is also recommended for pregnant individuals in late gestation. This maternal vaccination strategy aims to provide passive immunity to the newborn. By vaccinating the mother, her body produces RSV antibodies that transfer through the placenta to the developing baby, offering protection to the infant from birth through their first six months of life, when they are at highest risk for severe RSV disease.
RSV Immunity Across Different Age Groups
RSV immunity varies significantly across different age groups, reflecting unique vulnerabilities and immune responses. Infants and very young children are particularly susceptible to severe RSV disease due to their developing immune systems and smaller airways. For them, passive immunity strategies, such as maternal antibody transfer or monoclonal antibodies like nirsevimab, are important for protection during their most vulnerable months.
Older children and adults typically experience milder RSV infections after their initial exposure, often resembling a common cold. However, natural immunity is not long-lasting, leading to repeated infections throughout their lives. These subsequent infections usually do not result in severe outcomes, but the virus can still circulate within communities.
In contrast, older adults, especially those aged 60 and above, and immunocompromised individuals, face an increased risk of severe RSV disease despite prior exposures. This heightened vulnerability highlights the importance of active vaccination strategies in these populations. Vaccines like Abrysvo and Arexvy bolster their immune defenses, helping to prevent serious illness and hospitalizations.