For six decades, there was no approved vaccine for one of the most common causes of severe illness in infants, young children and older adults: RSV. Until now.
2023 has been a breakthrough year, with multiple vaccine and treatment approvals. On Monday, the U.S. Food and Drug Administration endorsed a vaccine for pregnant women — the first RSV vaccine to offer protection to vulnerable infants.
Among the scientists responsible for this discovery is Jason McLellan, a professor at UT Austin’s Department of Molecular Biosciences. Although most people are repeatedly infected with RSV throughout their lifetimes, McLellan said, it only poses a strong threat to certain groups.
“RSV causes significant disease in the very young and in the elderly,” he said. “For healthy adults, it's sort of a bad cold.”
According to the Centers for Disease Control and Prevention, RSV is the leading cause of hospitalization in infants. The agency estimates up to 80,000 kids under the age of 5 are hospitalized with RSV each year. Older adults are hospitalized in numbers ranging from 60,000 to 160,000 each year because of the virus, and between 6,000 and 10,000 die.
Despite these sobering statistics, McLellan says, RSV’s magnitude has not always been understood.
“Most of the time, when people were sick with RSV, they didn’t know it, and it was just sort of grouped as a ‘flu-like illness,’” he said. “It’s only been in the last decade or so with specific testing for RSV that it's been appreciated that many of these hospitalizations and deaths due to respiratory illness are actually due to RSV.”
A surge of advancement
A surge of cases during the 2022 winter RSV season also raised awareness of the common virus, McLellan said. Coincidentally, the timing coincided with a flurry of activity in the testing and development of vaccines and treatments.
By the end of last year, clinical trials for vaccines from a range of pharmaceutical companies were in their final phases. In May, GSK’s vaccine for adults over 60, called Arexvy, became the first RSV vaccine to receive FDA approval. Approval for Pfizer’s Abrysvo for older adults shortly followed. On Monday, Abrysvo was also approved for pregnant women between 32-36 weeks of gestation.
While these vaccines crossed the finish line around the same time, they all built on decades of work.
“RSV was first isolated from chimpanzees in 1956, and since then, there's been decades of research from many investigators trying to understand basic virology," McLellan said, "how the virus enters cells, what its proteins are, how it causes disease, how to make vaccines."
Several factors contributed to the long lead time before effective vaccines were approved. One was an ill-fated attempt to develop an RSV vaccine for infants in the 1960s, which ultimately made infants who received the drug more likely to become severely ill. Two died. That tragedy made researchers especially cautious about RSV vaccines for infants, McLellan said.
Additionally, he said, technology had to catch up. He and colleagues at the National Institutes of Health played a pivotal role in this advancement by developing a new way to engineer and stabilize proteins that certain viruses use to enter cells. This breakthrough also became foundational for the development of COVID-19 vaccines, the work McLellan is perhaps best known for.
What comes next?
Pfizer’s vaccine still needs to the greenlight from the CDC before it can be administered to pregnant women. Once it's approved, the FDA and CDC will continue to monitor the vaccine’s efficacy.
Ahead of the fall and winter RSV season, the CDC is recommending infants under eight months of age receive a new monoclonal antibody treatment that can help prevent infection. With this treatment, infants are given injections of antibodies, which can offer them protection before they are old enough to muster their own immune response.
Meanwhile, McLellan and colleagues in his lab at UT are at work addressing more viruses, including human metapneumovirus, another RSV-like virus that causes severe disease in the very young and the elderly. He’s also focused on other pathogens that might cause major outbreaks in the future.
“Vaccine development takes a long time,” he said. “There have been a lot of funders who are starting to put money toward how to make vaccines against different families of viruses. In case there is a large epidemic or pandemic in the future, we’ll already be ready.”
