The Food and Drug Administration on Wednesday approved Pfizer’s RSV vaccine for adults 60 years of age and older, making it the second shot for the common respiratory virus to reach market in the U.S.
Its clearance comes weeks after the regulator approved GSK’s similar vaccine Arexvy. Both shots are designed to protect against infections from RSV, or respiratory syncytial virus, which can cause serious illness in older adults, young children and people with weakened immune systems.
Their arrival represents a major medical advance after decades of prior research had failed to produce a safe and effective RSV vaccine. Now, older adults will soon have two protective options once the vaccines are made available.
An RSV vaccine “has been a long time coming,” Jayne Hornung, chief clinical officer at data and research firm Managed Markets Insight and Technology, wrote in an email.
“RSV can be life-threatening for older adults who may have other medical conditions or may be otherwise immunocompromised,” she added. The vaccines "will help protect these high-risk patients from [the] severe disease" the virus can cause.
Pfizer expects its shot, which will be sold as Abrysvo, to be available in the third quarter. Advisers to the Centers for Disease Control are scheduled to meet June 21 to discuss the two shots and develop recommendations for their use.
Pfizer’s and GSK’s approvals come after two March meetings of FDA advisers, who recommended clearance of both shots despite some concerns.
Pfizer’s application was based on results from a Phase 3 trial, which enrolled more than 34,000 adults and compared the company’s shot to a placebo in preventing RSV-associated disease. Trial results, which were first announced last August and published in April, showed 67% efficacy in preventing infections with at least two symptoms. Protection was even greater against more severe disease, defined as three or more symptoms of RSV-related illness.
At the meeting reviewing Pfizer’s candidate, FDA advisers had expressed some concern about potential risks associated with the vaccine, though.
Two trial participants in Pfizer’s study were diagnosed with a rare autoimmune disease known as Guillain-Barré syndrome, which affects a person’s nerves. The cases were judged to be possibly related to the vaccine, leading committee members to recommend a post-marketing study to further evaluate the shot’s safety and to list Guillain-Barré as a risk on its label. (While Abrysvo’s prescribing information notes the cases, the FDA did not add an explicit warning on Guillain-Barré.)
Committee members also noted Pfizer enrolled relatively few high-risk participants in its trial and did not extensively test the shot alongside a flu vaccine, presenting a potential blind spot for health officials as RSV and flu season usually coincide.
Ultimately, the committee backed Pfizer’s vaccine in two 7-4 votes in favor of its safety and efficacy.
Similar to GSK’s Arexvy, Abrysvo works by targeting a “prefusion” form of the virus’ F protein to stimulate an immune response. This breakthrough was initially made a decade ago by researchers at the National Institutes of Health, helping pave the way for the vaccines GSK and Pfizer have now brought to market.
That breakthrough also proved useful in designing vaccines for COVID-19, noted Barney Graham, former deputy director of the NIH’s vaccine research center, in a recent editorial published in The New England Journal of Medicine. “The success of structure-based vaccine design for RSV informed the rapid response to COVID-19.”
Pfizer is currently studying its shot’s safety when co-administered with other vaccines, such as for COVID and the flu. Lack of data could mean the shot is given separately, potentially limiting uptake, according to analysts.
Pfizer also aims to win approval of its vaccine for use in pregnant women as a way to confer protection to newborn infants.
Earlier this month, FDA advisors backed maternal use of the company’s vaccine, voting 14-0 in favor of its effectiveness and 10-4 in support of the shot’s safety. If approved, the shot would be given to women between 24 and 36 weeks pregnant. The FDA is expected to make a decision before August.