The safety of respiratory syncytial virus (RSV) vaccines is under continuous scrutiny across different age groups and populations, with ongoing monitoring by the Centers for Disease Control and Prevention (CDC) and the Food and Drug Administration (FDA). Recent data and clinical trials have provided insights into the safety profiles of various RSV vaccines, including those from GSK, Pfizer, and Moderna, as well as the nirsevimab passive immunization for infants.
Older Adults
Post-licensure safety data for GSK's Arexvy and Pfizer's Abrysvo RSV vaccines indicate a potential increased risk of Guillain-Barré syndrome (GBS) in adults aged 60 years and older. An FDA analysis estimated approximately 10 excess cases of GBS per 1 million vaccinated adults. While the association was statistically significant for the GSK vaccine, the Pfizer vaccine showed a similar but not statistically significant trend, possibly due to fewer administered doses. These findings have limitations, including potential misclassification of GBS cases, and further analyses are underway.
In clinical trials for Moderna's mResvia RSV vaccine, no cases of GBS were reported within 42 days post-vaccination. Post-licensure data for this vaccine is still being monitored.
Infants and Young Children
Clinical trials of nirsevimab, a passive immunization for infants and young children, have not raised significant safety concerns. However, post-licensure reports have identified rare cases of serious hypersensitivity reactions. As of October 2024, no new safety information has emerged that would alter the benefit-risk assessment of nirsevimab.
Pregnant Individuals
Clinical trials of Pfizer's Abrysvo RSV vaccine in pregnant individuals (24-36 weeks' gestation) revealed a non-statistically significant increase in preterm births. Consequently, the FDA approved the vaccine for use between 32 and 36 weeks' gestation to mitigate the potential risk of preterm birth before 32 weeks. A non-statistically significant increase in hypertensive disorders of pregnancy was also observed.
Preliminary findings from a Vaccine Safety Datalink (VSD) study indicated that RSV vaccination during 32-36 weeks' gestation was not associated with an increased risk of preterm birth or babies being born small for gestational age (SGA). Additional studies are ongoing to further investigate potential risks of high blood pressure issues, including pre-eclampsia.
Adults Aged 18-59
A Phase 3 randomized, double-blind, placebo-controlled trial (NCT05842967) assessed the safety and immunogenicity of the RSVpreF vaccine in adults aged 18-59 at high risk for severe RSV due to chronic medical conditions. Participants received either a single 120-mg dose of RSVpreF vaccine or placebo. The study, which included 678 participants, found that the proportion of adults aged younger than 60 who achieved a seroresponse was greater for both RSV-A (93.1% vs 88.0%) and -B (93.4% vs 85.0%) compared to those aged 60 and older. More local reactions were reported by recipients of RSVpreF (36.6%) vs placebo (11.6%), while systemic event rates were similar between the RSVpreF (57.4%) and placebo (55.6%) groups. The most common local reaction was injection-site pain (35.3% in the RSVpreF group vs 10.7% in the placebo group), and the most common systemic event was fatigue (37.3% in the RSVpreF group vs 38.2% in the placebo group). No vaccine-related serious adverse events or newly diagnosed chronic medical conditions were reported. The researchers concluded that the study results support the expansion of the RSVpreF indication for prevention of RSV-associated LRTI to include adults 18 through 59 years of age with risk factors for severe RSV, thereby fulfilling the important unmet need in this population.
