FDA Greenlights a Second RSV Vaccine for Older Adults

The Food and Drug Administration (FDA) approved Pfizer’s vaccine against respiratory syncytial virus, or RSV, for adults 60 and older earlier this week. This marks the second available RSV vaccine in the United States after a version from pharmaceutical company GSK earned approval last month.

Pfizer’s vaccine, called Abrysvo, is designed to prevent lower respiratory tract disease caused by RSV. The illness causes mild, cold-like symptoms in most people, but it can be severe and even deadly for high-risk groups like young children and older adults. 

Record-high RSV cases collided with influenza and COVID-19 to cause what some public health experts called a “tripledemic” of respiratory illness last winter. Children were hit particularly hard; babies under a year old were hospitalized at a rate more than 10 times as high as the same point in 2019.

However, older adults are also susceptible to serious disease and death from RSV. The CDC estimates RSV is responsible for at least 177,000 hospitalizations and 14,000 deaths among U.S. adults each year.

“We’ve learned that RSV often is serious as influenza in causing serious respiratory disease in older persons year in and year out,” William Schaffner, MD, the medical director of the National Foundation for Infectious Diseases and a professor of infectious diseases at the Vanderbilt University School of Medicine, told Verywell. “So having some vaccines available for the prevention of RSV in older persons, is really a great advance.”

Results from a phase 3 clinical trial of more than 34,000 participants aged 60 and older showed a single dose of Pfizer’s vaccine was nearly 67% effective at preventing RSV cases with at least two symptoms, and 86% effective at preventing cases with at least three symptoms.

The single-dose vaccine works by blocking a key protein that helps the virus to invade human cells. 

The vaccine’s effectiveness appears on par with GSK’s RSV vaccine, which was nearly 83% effective at preventing lower respiratory disease in clinical trials.

Both companies say their vaccines will be available ahead of the next RSV season, which begins in early fall. In a meeting next month, a panel of advisors to the CDC will meet to discuss RSV vaccine recommendations to health providers.

So far, research shows both vaccine candidates are safe, with injection site pain, muscle stiffness, and fatigue listed as the most common side effects.

In an FDA meeting March 1, panelists discussed a seemingly increased risk of autoimmune dysfunction that could be related to the vaccine. In Pfizer’s clinical trial, there was one case of Guillain-Barré syndrome and one case of a rare variant of that syndrome, called Miller Fisher syndrome. These serious adverse events were rare, representing one case for every 9,000 participants. However, that’s higher than the one to two people per 100,000 typically diagnosed with Guillain-Barré each year.

The general consensus of the advisory committee, Schaffner said, was that this data could amount to a “statistical fluke.” The panel voted 7-4 to recommend the vaccine’s approval. Schaffner said he expects that the CDC will agree with the FDA that the vaccine is safe for older adults.

Young children were hit particularly hard in the last RSV season. Regulators are also reviewing RSV protection for kids, including a maternal vaccine by Pfizer and a monoclonal antibody for infants. 

There are more RSV vaccines in the pipeline for older adults, too. Moderna said it expects to submit data on its mRNA vaccine for RSV in seniors in the next few months. Bavarian Nordic also said it will report results from a phase 3 trial of its vaccine this year. 

“Vaccines don’t prevent disease—vaccination prevents disease,” Schaffner said. “Now we have to figure out how to get these RSV vaccines out of the refrigerator and into the arms of older persons on a regular basis. That will be a challenge going forward.”