Respiratory Syncytial Virus (RSV) is a highly contagious pathogen that usually causes mild, cold-like symptoms in healthy individuals. However, RSV poses a significant health threat to vulnerable populations, particularly infants and older adults, often leading to severe lower respiratory tract disease, hospitalization, and sometimes death. Several preventative options have been developed to mitigate this risk. Understanding the safety profile of these interventions is necessary for anyone considering protection against RSV.
Defining the Available Products and Recipients
Strategies for RSV prevention fall into three categories, each designed for a specific at-risk population.
The first category includes vaccines intended for older adults, typically those aged 60 years and older. Some products are also available for adults aged 50 to 59 with underlying medical conditions. These adult vaccines stimulate the recipient’s immune system to produce protective antibodies.
The second category is the maternal vaccine, administered to pregnant individuals, usually between 32 and 36 weeks of gestation. This vaccination transfers protective antibodies across the placenta to the fetus, providing the newborn with passive immunity immediately after birth.
The final strategy involves a monoclonal antibody injection. This is not a traditional vaccine but a form of passive immunization given directly to infants and some high-risk toddlers. This antibody provides immediate, temporary defense against the virus for the entire RSV season.
Common and Expected Side Effects
The majority of reactions experienced after any form of RSV immunization are mild, localized, and transient. The most frequently reported reaction across all age groups is pain, tenderness, or swelling at the injection site, which usually resolves within a couple of days.
Many recipients also report systemic symptoms, such as fatigue, headache, and muscle or joint aches. Less common expected reactions include a low-grade fever or mild nausea, particularly in older adults. These systemic effects are generally short-lived, lasting no more than 24 to 48 hours, and are comparable to the temporary discomfort experienced after other routine immunizations.
Rare Severe Adverse Events
The safety profile of RSV prevention methods includes monitoring for rare but serious adverse events. An immediate, severe allergic reaction, known as anaphylaxis, is a potential risk with any vaccine or injectable medication. Anaphylaxis is extremely rare, and healthcare providers administering the injection are prepared to treat it immediately.
A condition specifically monitored with the adult RSV vaccines is Guillain-Barré Syndrome (GBS), a rare disorder where the immune system attacks the peripheral nerves. Post-marketing surveillance suggests a potential increased risk of GBS within 42 days following vaccination in adults aged 65 and older. This increased risk is very small, estimated at approximately seven to nine excess cases of GBS per million doses administered in this older population.
For the maternal vaccine, clinical trial data identified a slight imbalance in the rate of preterm births compared to the placebo group, though this difference was not statistically significant. Regulatory bodies approved the maternal vaccine for a narrower gestational window of 32 through 36 weeks to address this potential signal. This timing provides the infant with protective antibodies while avoiding the risk of very early preterm birth. Monitoring for potential long-term maternal or infant complications, including preeclampsia, continues as real-world data becomes available.
Warnings and Contraindications
Certain circumstances require delaying or foregoing an RSV preventative measure to ensure safety.
The absolute contraindication for any RSV product is a history of a severe allergic reaction to a previous dose or to any component of the product itself. Individuals must disclose any known allergies to their healthcare provider before administration.
A general precaution is to postpone the immunization if the individual has an acute moderate or severe illness, especially one accompanied by a fever. This delay avoids mistakenly attributing symptoms of the underlying illness to the immunization. Minor illnesses, such as a common cold without fever, typically do not require postponement.
Bleeding Risk Considerations
For the monoclonal antibody given to infants, injection site bleeding is a consideration for children with clinically significant bleeding disorders. Adults taking blood-thinning medication should also inform their provider, as the injection may cause a larger bruise or hematoma at the site. These situations require a discussion with a healthcare professional to determine the safest approach before proceeding.