The Food and Drug Administration on Wednesday approved the first vaccine to prevent infections caused by respiratory syncytial virus, or RSV, a widespread pathogen that can be deadly in young children and older adults.

Approval of the vaccine, which was developed by GSK, represents a research milestone after decades of unsuccessful efforts to develop an effective shot for the virus. It could be followed later this month by another RSV vaccine, from Pfizer, that’s under FDA review.

RSV is a leading cause of respiratory illness, often overlapping in seasonal patterns with influenza and, recently, COVID-19. Each year, hundreds of children under 5 years old and thousands of older adults die from RSV infections in the U.S. Many more are hospitalized.

GSK’s shot, called Arexvy, is cleared only for use in adults 60 years or older. The company has not yet disclosed a specific price, but executives have previously indicated they will charge between $60 and $185 a dose, around what vaccines for influenza and shingles cost. 

“The advent of a new vaccine that will help diminish the impact of particularly serious aspects of RSV is really something that we're all looking forward to,” said Bill Schaffner, medical director of the National Foundation for Infectious Diseases and a professor at the Vanderbilt University, in an interview before the FDA’s decision.

In a statement, Peter Marks, head of the FDA office that reviews vaccines, called Arexvy an "important public health achievement."

"Older adults, in particular those with underlying health conditions, such as heart or lung disease or weakened immune systems, are at high risk for severe disease caused by RSV," he added.

Drugmakers have sought to develop a preventive shot for RSV since the 1950s. But research, which focused primarily on infants and children, faltered after tests in the 1960s of one type of vaccine showed it exacerbated infections. Later efforts also came up short.

Then in 2013, a breakthrough by researchers at the National Institutes of Health gave drugmakers a better blueprint for an effective vaccine. Scientists there showed that designing a vaccine against the virus’ “F” protein, but before its shape changes to fuse with human cells, would produce a stronger immune response.

GSK’s vaccine targets this “prefusion” F protein to spur an immune response against RSV infection, as does Pfizer’s shot. Moderna and Bavarian Nordic, which are following close behind in development of their own RSV vaccines, also target the prefusion F protein, among others. (Johnson & Johnson was among these frontrunners until March, when it abandoned its experimental shot and halted a large late-stage trial.)

The advances in RSV research later helped scientists in their efforts to design a vaccine for COVID.

“Work that had taken decades in RSV research was compressed into just a few weeks for SARS-CoV-2, providing sequences, structures, and reagents needed to rapidly develop safe and effective vaccines and therapeutic monoclonal antibodies,” wrote Barney Graham, an author on that NIH research and former deputy director of the institute’s vaccine research center in an editorial published in The New England Journal of Medicine.

GSK’s approval application was supported by several clinical trials involving older adults. The company’s main study enrolled roughly 25,000 people across 17 countries who were given either GSK’s shot or a placebo.

Results, published in February, showed that vaccination reduced the risk of RSV-related lower respiratory tract disease by 83% compared to placebo. Protection was higher against more severe disease, reaching 94% in adults over 60. The shot provided coverage against both the A and B strains of the virus, data showed.

Overall, reactions to vaccination were generally mild or moderate in severity and were most commonly injection site pain and fatigue. Study investigators reported one case of the immune syndrome disorder Guillain-Barré and two cases of a type of central nervous system inflammation called acute disseminated encephalomyelitis. One of those two individuals died.

At a March meeting convened by the FDA, a group of independent experts voted 10-2 in favor of the vaccine’s safety, and unanimously agreed that GSK’s data were supportive of its effectiveness.

The same advisory committee also discussed the safety and efficacy of Pfizer’s vaccine and, while they supported it as well, they raised more concerns about its side effect risk.

The committee, which is made up of vaccine and infectious disease specialists, were encouraged by GSK’s testing its vaccine alongside an influenza vaccine, as well as in people with weakened immune systems. In the company’s large study, about 39% of participants had underlying conditions that put them at risk of more severe disease.

Pfizer did not formally study co-administration of its shot with an influenza vaccine, which the experts flagged as a concern because both are likely to be given around the same time each year.

RSV has long been treated as a pediatric infection since most children are exposed by age 2. But further research has emphasized RSV’s risk to older adults.

With a vaccine finally available, medical physicians and experts will have to learn “that RSV is yet another winter viral infection that rivals the importance of influenza,” Schaffner said.

As a vaccine, Arexvy is meant to prevent RSV-associated disease, rather than ease existing infections, which are treated with fever and pain reducers. An antiviral medicine is currently being tested in adults.

“Each year, our hospitals and clinics and emergency rooms are, of course, stressed with patients coming in with these respiratory infections,” Schaffner said. “The more we can prevent them, we can reduce the stress on the healthcare system, as well as protecting these individuals.”

With the FDA’s approval, experts at the Centers for Disease Control and Prevention will be tasked with putting together recommendations for the vaccine’s general use. They’re next set to meet in late June.

GSK is currently conducting additional tests of its vaccine’s safety and plans to provide additional data in high-risk adults between 50 to 59 years of age. As part of the FDA’s approval, the agency is requiring GSK study the risks of Guillain-Barré and acute disseminated encephalomyelitis specifically.

The company halted clinical testing of its maternal RSV candidate in February of last year. GSK did not go into much detail about the pause, but said further analysis of the safety data from the trials is “ongoing.”

Last month, Pfizer published study results supporting its vaccine’s use in pregnant women, and the FDA has scheduled an advisory panel meeting for later this month to weigh in. Vaccination of the mother is meant to protect infants from RSV infection through 6 months of age.

GSK has predicted its vaccine will earn “multi-billion” dollar sales, similar to its top-selling shingles vaccine Shingrix. The company has millions of doses ready to be shipped and has begun laying the groundwork via marketing campaigns aimed at RSV awareness, including one that involves former National Basketball Association star and public health advocate Earvin “Magic” Johnson.

Educating the public and medical community will be the next hurdle, according to Schaffner.

“Getting the vaccine is the beginning,” he said. “It's not the end of story.”

Editor’s note: This story has been updated to include previous GSK comments about the vaccine’s price.