The year brought significant advancements in the prevention and treatment of respiratory syncytial virus (RSV), marked by new vaccine approvals, expanded indications, and promising monoclonal antibody therapies. These developments offer enhanced protection for vulnerable populations, including older adults and infants, against severe RSV-related illness.
Vaccine Approvals and Expansions
Moderna's mRNA-1345 RSV vaccine (mResvia) received FDA approval in May for adults aged 60 and older, based on the ConquerRSV trial. The trial demonstrated an efficacy of 83.7% in preventing RSV-associated lower respiratory tract disease (LRTD) with at least two signs or symptoms and 82.4% efficacy against LRTD with at least three signs or symptoms.
GSK's Arexvy saw its approval expanded in June to include adults aged 50-59 at increased risk of LRTD due to underlying chronic conditions. Previously, it was only approved for those 60 and older. Pfizer's Abrysvo also had its approval expanded in October to include adults aged 18-59 with comorbidities placing them at high risk for RSV-related LRTD. It was already approved for adults 60+ and pregnant individuals to protect infants.
Updated Vaccination Recommendations
The CDC's Advisory Committee on Immunization Practices (ACIP) revised its recommendations for adult RSV vaccination in June. The updated guidance advises a single dose of RSV vaccine for all adults aged 75 and older. Adults aged 60-74 at increased risk of severe RSV disease may also receive a vaccine, according to the committee's decision. However, ACIP did not vote on recommending the vaccines for younger at-risk groups.
Maternal Vaccine Safety and Efficacy
Real-world data provided reassurance regarding the safety of maternal RSV vaccines. A study found that Pfizer's maternal RSV vaccine did not increase the risk of preterm birth or other adverse neonatal outcomes. Specifically, preterm birth occurred in 5.9% of women who received the vaccine compared to 6.7% without it (adjusted OR 0.87, 95% CI 0.62-1.20). While GSK abandoned its maternal RSV vaccine development in 2022 due to preterm birth risks, the FDA recommends Pfizer's vaccine be administered between 32-36 weeks of gestation to mitigate potential risks.
Monoclonal Antibody Advancements
Nirsevimab (Beyfortus), a monoclonal antibody, demonstrated strong protection against RSV in infants. The ENVIE study showed an estimated 83% effectiveness in preventing hospitalization from RSV bronchiolitis (95% CI 73.4-89.2) in infants younger than 12 months. Another CDC study indicated 90% effectiveness in preventing RSV hospitalizations in infants, though researchers cautioned that the study period covered only part of a typical RSV season.
Furthermore, the investigational monoclonal antibody clesrovimab showed promising results in protecting against RSV-related disease in healthy preterm and term infants. A single intramuscular dose of clesrovimab reduced the incidence of RSV-associated medically attended lower respiratory infections by 60.4% (95% CI 44.1-71.9, P < 0.001) and RSV-associated hospitalizations by 84.2% (95% CI 66.6-92.6, P < 0.001) through 5 months.
Guillain-Barré Syndrome (GBS) and RSV Vaccines
Reports of Guillain-Barré syndrome (GBS) following RSV vaccination in adults aged 60 and up were rare but higher than expected. VAERS data showed 1.5 reports of GBS per 1 million doses of GSK's RSV vaccine and five reports per 1 million doses of Pfizer's RSV vaccine. Despite these reports, the CDC maintains that the benefits of RSV vaccination outweigh the small risk of GBS.
