Respiratory Syncytial Virus (RSV) is a highly prevalent respiratory pathogen responsible for annual outbreaks, often presenting as a common cold in healthy individuals. Contracting RSV “back to back” is not only possible but is an expected feature of the virus. Unlike many infections that confer long-lasting protection, the body’s immune response to RSV is generally incomplete and wanes quickly. This characteristic means that reinfection is a common occurrence across all age groups, sometimes even within the same RSV season.
The Nature of RSV Immunity
The primary reason for recurrent infections is that the immunity generated after a natural RSV infection is neither sterilizing nor robust. The body’s initial defense often fails to create a strong, durable immunological memory capable of completely blocking the virus upon re-exposure. Studies have shown that a significant portion of adults can become reinfected with the same strain of RSV just two to eight months after an initial infection.
Protection from reinfection is short-lived because the neutralizing antibodies produced in response to the virus, particularly those targeting the fusion (F) and attachment (G) proteins, decline rapidly. This decay in circulating antibodies leaves the respiratory tract vulnerable to viral re-entry. Furthermore, the virus circulates as two main groups, A and B, which have slight antigenic differences. Encountering a different strain group can bypass the partial protection gained from a previous infection, contributing to frequent reinfections.
The cellular immune response, involving T-cells, also appears insufficient to prevent reinfection. While T-cells are activated during the primary infection, subsequent re-exposure does not consistently boost this specific T-cell memory. This lack of sustained cellular and humoral protection makes repeated infections a lifelong reality.
Factors Influencing Reinfection Severity
The clinical outcome of an RSV reinfection varies depending on the age and overall health of the person. For most healthy adults, a second or third RSV infection typically presents as a mild upper respiratory illness, indistinguishable from a common cold. Symptoms may include a runny nose, sore throat, cough, and low-grade fever, rarely progressing to severe disease.
Infants and young children face a higher risk of severe disease during their first infection due to their small airways and immunologically immature systems. While subsequent infections tend to be less severe than the first, they can still lead to significant illness, such as bronchiolitis or pneumonia, especially in those with underlying conditions. The risk of severe illness upon reinfection remains higher for children who experienced their first RSV infection when they were younger than six months old.
The elderly, generally defined as individuals 60 years of age and older, represent another population where reinfection can be severe. As the immune system naturally wanes with age, the protection gained from prior exposure diminishes, increasing their susceptibility to serious outcomes. Reinfection in this age group can result in severe lower respiratory tract infections, including pneumonia, or can exacerbate chronic conditions like congestive heart failure and Chronic Obstructive Pulmonary Disease (COPD). Immunocompromised individuals of any age also remain at high risk for severe, prolonged illness.
Prevention and Protection for High-Risk Individuals
Given the predictable nature of RSV reinfection and the risk to vulnerable groups, several targeted medical interventions are now available. For infants, two primary methods offer passive immunity: maternal vaccination and monoclonal antibody products. Pregnant individuals are recommended to receive an RSV vaccine, such as Abrysvo™, between 32 and 36 weeks of gestation during the RSV season. This allows the mother to produce antibodies that are then transferred across the placenta, providing immediate protection to the newborn.
Alternatively, infants can receive a long-acting monoclonal antibody product, such as nirsevimab (Beyfortus™), which provides ready-made antibodies. A single intramuscular dose of nirsevimab is recommended for all infants under eight months old who are entering their first RSV season, and for high-risk children up to 24 months entering their second season. This passive immunization offers protection for approximately five months, covering the entire typical RSV season.
Older adults, particularly those aged 60 and above, can receive an RSV vaccine to stimulate their own immune system to generate a protective response. For those between 50 and 74 with underlying chronic medical conditions, vaccination may also be recommended. General preventative measures, such as frequent handwashing, sanitizing surfaces, and avoiding close contact with sick individuals, remain important in high-risk environments to limit the spread of the virus.