Manhattan, NY—Even though immunization against RSV among older adults remains relatively low at around 24% as of late March, that is not for lack of efficacy.
In fact, new information on vaccine efficacy and safety data on the bivalent RSV prefusion F vaccine, marketed as Abrysvo by Pfizer, Inc., showed strong vaccine efficacy after two seasons for adults aged 60 years and older.
That was based on results from the announced top-line Abrysvo vaccine efficacy and safety data for RSV in adults aged 60 years and older following a second season in the Northern and Southern Hemispheres from the ongoing pivotal phase III clinical trial RENOIR (RSV Vaccine Efficacy Study in Older Adults Immunized against RSV Disease). Pfizer announced that vaccine efficacy against RSV-associated lower respiratory tract disease (LRTD), defined by three or more symptoms, after disease surveillance in season two was 77.8% (95.0% CI: 51.4, 91.1); vaccine efficacy following season one was 88.9% (95.0% CI: 53.6%, 98.7%), which demonstrates durable efficacy after two seasons.
“Consistent vaccine efficacy was demonstrated for both RSV A and RSV B after season two with vaccine efficacy against each subtype of ≥80% for LRTD with three or more symptoms,” according to the report. “Vaccine efficacy was also sustained against less severe LRTD, defined by two or more symptoms, from 65.1% (95.0%% CI: 35.9%, 82.0%)1 after season one to 55.7% (95.0% CI: 34.7%, 70.4%) after the end of season two. Vaccine efficacy against RSV-associated LRTD, defined by three or more symptoms, across both seasons after approximately 16.4 months of disease surveillance was 81.5% (95.0% CI: 63.3, 91.6).”
The manufacturer said that no new adverse events were reported through the second RSV season beyond the clinical trial during the first season. Pfizer is conducting postmarketing studies and surveillance programs on the safety of Abrysvo. The FDA has said syncope might occur in association with administration of injectable vaccines, including Abrysvo, and that immunocompromised individuals, including those who are receiving immunosuppressive therapy, could have a diminished immune response to the vaccine. Specific to the vaccines use in expectant mothers is a concern about the possibility of preterm birth.
For the 2023–2024 respiratory virus season, the CDC’s Advisory Committee on Immunization Practices recommended RSV vaccines for adults aged 60 years and older (using shared clinical decision-making).
Pfizer is currently the only company with an RSV vaccine to help protect older adults, as well as infants through maternal immunization. The other RSV vaccine approved for older adults is Arexvy from GSK.
In May 2023, the FDA approved Abrysvo for the prevention of LRTD caused by RSV in individuals aged 60 years or older. That was followed in September by the approval of maternal immunization to protect infants.
Pfizer has also initiated an additional clinical trial evaluating the vaccine in adults, specifically focusing on those aged to 59 years at higher risk for RSV due to underlying medical conditions such as asthma, diabetes, and chronic obstructive pulmonary disease, as well as adults aged 18 years and older who are immunocompromised and at high risk for RSV.
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