WASHINGTON — The Food and Drug Administration this week approved Pfizer’s Abrysvo for prevention of respiratory syncytial virus lower-respiratory-tract disease in adults age 60 and older, giving the United States a second vaccine against a virus that sends tens of thousands of older adults to hospitals each year. The May 31 decision caps decades of attempts to create an effective RSV vaccine and sets up the first fall season in which older Americans could have more than one approved immunization option.

Pfizer’s approval announcement said the decision was based principally on the Phase 3 RENOIR trial, which enrolled approximately 37,000 adults age 60 and older. Abrysvo is a bivalent, unadjuvanted vaccine containing stabilized prefusion F proteins designed to generate antibodies against both major RSV subgroups.

A long-running vaccine problem reaches a second solution

RSV is best known for severe disease in infants, but its burden in older adults is substantial. Age-related changes in immunity and chronic heart and lung disease can turn what begins as a respiratory infection into pneumonia, bronchiolitis, hospitalization or death. The FDA approved GSK’s Arexvy on May 3, describing it in an agency announcement as the first RSV vaccine licensed in the United States for adults 60 and older. Abrysvo arrives less than a month later, creating competition in a category that did not exist at the beginning of May.

The scientific breakthrough behind both programs is the ability to stabilize RSV’s fusion protein in its prefusion shape. That form exposes highly vulnerable targets to the immune system and produces potent neutralizing antibodies. Earlier RSV vaccine efforts struggled in part because the relevant protein changes shape as the virus enters cells, making it difficult to present the immune system with the most protective target.

RENOIR shows strongest protection against more symptomatic disease

Results from the RENOIR trial were published in the New England Journal of Medicine. In the interim analysis, vaccine efficacy against RSV-associated lower-respiratory-tract illness with at least two symptoms was 66.7%, while efficacy against illness defined by at least three symptoms was 85.7%. The findings suggest stronger protection against more clinically substantial disease, although longer follow-up is needed to determine durability across multiple RSV seasons.

Pfizer had initially reported those figures in an August 2022 analysis, which allowed the company to move toward regulatory submission. The trial was randomized and placebo-controlled, with participants followed for RSV disease and safety outcomes.

Advisers supported efficacy but scrutinized safety

FDA’s Vaccines and Related Biological Products Advisory Committee reviewed the application during its February 28 meeting. Outside experts voted 7-4, with one abstention, that available evidence supported effectiveness and separately 7-4 that it supported safety. Pfizer’s account of the vote highlighted the efficacy results while acknowledging the committee’s separate consideration of safety signals.

Among the issues discussed were rare neurologic events, including cases of Guillain-Barré syndrome reported in temporal association with vaccination. Such uncommon events are difficult to characterize definitively even in a trial involving tens of thousands of people, so post-licensure surveillance will be important as the vaccine moves into broader use.

The approval is specific to older adults

FDA’s approval letter licenses Abrysvo for prevention of lower-respiratory-tract disease caused by RSV in individuals 60 years of age and older. Pfizer is separately studying the same prefusion-F platform for maternal immunization intended to protect infants after birth, but that indication remains under FDA review and is not part of this week’s approval.

That distinction matters for clinicians and patients. The adult vaccine decision does not create a universal recommendation for every person over 60; recommendations on who should receive the vaccine and how it should be incorporated into routine care will depend on the Centers for Disease Control and Prevention and its Advisory Committee on Immunization Practices. Factors such as age, chronic disease, immune status and timing before the RSV season are likely to shape those discussions.

A new prevention market takes shape before fall

The rapid approvals of Arexvy and Abrysvo change the prevention landscape for a virus that previously had no licensed vaccine. For manufacturers, the competition will center on effectiveness, durability, safety, coadministration with influenza and COVID-19 vaccines, supply and payer coverage. For public-health officials, the challenge is more practical: identifying the older adults most likely to benefit and communicating how RSV vaccination fits with an already crowded seasonal immunization schedule.

The significance of this week is not that RSV has suddenly become easy to prevent. It is that after decades of scientific setbacks, the United States now has two licensed vaccines for older adults within the same month. Abrysvo’s approval converts the RENOIR trial’s efficacy signal into a clinical option and moves RSV prevention from a long-standing research goal into real-world implementation.