FDA Approves Pfizer RSV Vaccine for Older Adults

Lori Youmshajekian

June 01, 2023

The US Food and Drug Administration (FDA) has approved another vaccine that protects adults older than 60 years from respiratory syncytial virus (RSV).

Abrysvo, made by Pfizer, is an nonadjuvanted vaccine that contains two prefusion F proteins designed to protect against the A and B strains of RSV. The vaccine is indicated for the prevention of lower respiratory tract disease caused by RSV, according to a press release from the company.

The approval is based on data from the ongoing RENOIR clinical trial, which involved about 37,000 participants. The randomized, double-blind, placebo-controlled trial investigated the safety of the vaccine and its efficacy against lower respiratory tract illness and acute respiratory illness associated with RSV infections.

Approximately half of the participants received a single 120-μg dose of the vaccine by intramuscular injection; the other half received a placebo injection.

The vaccine was about 67% effective against RSV-associated lower respiratory tract illness with two symptoms and almost 86% effective against cases with three or more symptoms, according to data from an interim analysis published in April in The New England Journal of Medicine. Researchers also documented 62% efficacy against RSV-associated acute respiratory illness.

The most commonly reported side effects were pain at the injection site, fatigue, headache, and muscle pain. One case of Guillain-Barré syndrome and one case of Miller-Fisher syndrome were reported among the recipients of the vaccine.

Immunocompromised people were not included in the trial, which the researchers cited as a limitation of their study.

The trial follows a phase 2a study in which healthy adults aged 18 to 50 years were randomly assigned to receive either a single injection of the vaccine or a placebo. After participants were inoculated with a challenge virus, 6% of the vaccinated group developed symptomatic infection, compared with 48% of the group that received placebo, according to results published last June.

RSV sends between 60,000 to 160,000 adults over age 65 in the United States to the hospital each year and causes up to 10,000 deaths annually in that age group, according to the Centers for Disease Control and Prevention (CDC). Older adults with underlying conditions or a weakened immune system are at higher risk for severe disease.

Young children are also particularly vulnerable to the virus. Up to 80,000 annual hospitalizations and up to 300 deaths are caused by RSV among children younger than age 5, according to the CDC.

The approval is the second in the past month for a vaccine that targets RSV. GlaxoSmithKline obtained FDA approval for Arexvy on May 3 ― the first ever immunization for the virus. Moderna is also set to file for approval of its RSV vaccine for older adults in the coming months.

Earlier in May, the FDA Advisory Committee for vaccines voted to support the approval of Pfizer's RSV vaccine for infants through maternal immunization.

Pfizer expects the vaccine for older adults to be available ahead of the fall season of RSV, according to the company. Researchers will continue to collect efficacy data via the RENOIR trial for another RSV season.

The CDC committee of advisors are set to make recommendations for both the Pfizer and GSK vaccines at a meeting on June 21.

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