A Win for Adult RSV Vaccination Amid Vaccine Uncertainty, Hesitancy

Amid uncertainty about the future of federal vaccine policy, the committee of outside experts that advises the Centers for Disease Control and Prevention (CDC) on vaccines voted unanimously last week in favor of lowering the age at which adults should get vaccinated against respiratory syncytial virus (RSV).

The committee, called the Advisory Committee on Immunization Practices (ACIP), voted on April 16 in favor of recommending RSV vaccination for people ages 50-59 who have risk factors for having a severe case of RSV. The current recommendation is that those who are 60 to 74 with risk factors should be vaccinated against RSV and that everyone 75 and older should be, regardless of whether they have risk factors for a severe case. The long list of risk factors for severe RSV includes having cardiovascular disease; a chronic lung condition such as chronic obstructive pulmonary disease or asthma; diabetes with complications or requiring treatment with insulin or sodium-glucose cotransporter-2 (SGLT2) inhibitor; and severe obesity (a body-mass index of 40 or greater).

Data presented at the ACIP meeting showed that about a third of people between the ages of 50 and 59 would be eligible for the vaccine because they have one of those risk factors. A more liberal definition would increase the proportion to 43% of that age group. Although the ACIP work group on RSV adult vaccination is reviewing the evidence for revaccination, the current CDC recommendations call for a single shot of the RSV vaccine.

Albert C. Shaw, M.D., Ph.D.

The RSV work group is also considering data concerning broadening the RSV vaccination recommendations even further to include all adults with risk factors. Albert C. Shaw, M.D., Ph.D., chair of the work group, a professor at Yale School of Medicine and a voting member of ACIP, said a review of that data would be presented at the ACIP scheduled for June 25 and 26.

The FDA has approved three adult RSV vaccines: GSK’s Arexvy, Prifizer’s Abrysvo and Moderna’s mResvia. Arexvy is approved for use in the 50-59 age group, and Abrysvo is approved for use in all adults and in pregnant women as a way of protecting their infants from RSV vaccines. Currently, mResvia is approved only for those 60 and older, but Moderna has applied for FDA approval for its use in adults ages 18-59. That application’s Prescription Drug User Fee Act date — the date by which the FDA is supposed to decide whether to approve a drug or not — is June 12, 2025.

The questions swirling around the direction of federal vaccine policy stem from HHS Secretary Robert F. Kennedy Jr.’s history of casting doubt on the efficacy and safety of vaccines and the validity of the studies supporting them. Kennedy’s focus, though, has been on childhood vaccines. A more immediate issue is that the CDC is currently without a Senate-confirmed director after President Donald Trump withdrew the nomination of David Weldon and nominated Susan Monarez, the acting CDC director, instead. The decision on whether to accept the ACIP recommendation so it is part of the CDC’s official vaccine schedule may fall to Kennedy in the absence of a confirmed CDC director.

‘Immunobridging’ studies

At the ACIP meeting last Wednesday, Michael Melgar, M.D., a medical officer in the CDC’s Coronavirus and Other Respiratory Viruses Division and one of the co-leads of the ACIP work group for RSV in adults, went over the evidence for the three vaccines for the committee. He stressed that the work group’s recommendations were not specific to a particular vaccine, and, in some cases, he combined the results for all three to make a generalization about RSV vaccination.

Melgar noted that no manufacturer has conducted an efficacy study of their products in the 50-59 age group, so the evidence in support of lowering the age threshold for vaccination from 60 to 50 is derived from “immunobridging" studies that base estimates of efficacy on the results of studies of the vaccines effects on antibody levels and efficacy in the age groups they have been tested.

Melgar showed data that show that all three vaccines stimulate a bigger boost in neutralizing antibody levels in the 50-59 age group than in the older age groups. The relative increase was higher from the Abrysvo shot than it was from Arexvy or mResvia. Results of a calculation that lumped the three vaccines together showed that the vaccines were 69.3% effective against “medically attended” cases of RSV and 76.7% effective against hospitalization.

2,000 fewer hospitalizations

Like many vaccines, the RSV vaccines are, on rare occasions, associated with development of Guillain-Barré syndrome (GBS), an autoimmune reaction to the vaccine that results in an attack on peripheral nerves that can cause weakness, numbness or, in the worst cases, paralysis. In early January 2025 FDA required GSK and Pfizer to put a warning about GBS on their vaccines. Melgar said claims data suggest that that there were nine excess (above the background rate) cases of GBS per million doses of Abrysvo and seven per million doses of Arexvy. He noted that there was no data linking mResvia to GBS.

Source: Advisory Committee on Immunization Practices, RSV Work Group, April 16, 2025, ACIP meeting

Using the results of cost-effective research presented at the ACIP meeting along with the GBS figures, Melgar shared the results of calculations that show that a million doses of the Abrysvo and Arexvy (mResvia was not included in this particular calculation) would result in 2,000 fewer hospitalizations over three RSV seasons, 430 fewer admissions to intensive care units,and 130 fewer deaths. The calculations also show a million doses would result in between 0 and 18 additional cases of GBS.

American Academy of Family Physicians on board

In an interview last week after the ACIP vote, Jen Brull, M.D., president of the American Academy of Family Physicians and a family physician in Fort Collins, Colorado, heralded the RSV vaccine recommendation as an important development. The academy has its own process for deciding on vaccine recommendations, but Brull said there is every reason to believe it will follow ACIP’s lead.

Jen Brull, M.D.

Brull said the AAFP “is strongly in support of all evidence-based vaccines, and this appears to be an evidence-based recommendation, and we'll do our due diligence to confirm that we agree with the science that was evaluated by the ACIP.”

This ACIP meeting had been scheduled for February. When it was taken off the calendar (and only later rescheduled for April), the academy was one of several organizations that raised concerns about cancellation. If the ACIP’s recommendation on RSV isn’t officially adopted as CDC policy soon, Brull said she was sure the academy would speak out again. “If we see a similar delay in that process, I am confident that the AAFP [American Academy of Family Physicians] will continue to advocate for the truth of vaccines and the importance of recommendations to be sent forward. Will that happen? I don't know. That's what we are all wondering these days,” Brull said

Brull said she was concerned about vaccine hesitancy, noting that vaccine rates against measles had dropped below levels that curtail the spread of the virus. She referenced Kennedy’s past positions but commented that vaccine hesitancy has many causes, including interruptions in school and other schedules during the COVID-19 epidemic. “So we have a big job,” Brull said. “The great thing is that family doctors see everybody in the United States, and we're pretty good at that job in terms of making sure that people understand how safe vaccines are, how effective they are, and how important they are.”

But Brull also pointed to the worrying trend of a national shortage of primary care physicians.