The Atlantic The COVID shots—and new ones for RSV—herald a new era for designing vaccines. very fall, when the air turns chilly and the leaves red, pediatric ICUs begin preparing for the onslaught of the virus known as RSV. Not flu, not COVID, but RSV, or respiratory syncytial virus, is the No. 1 reason babies are hospitalized, year after year. Their tiny airways can become inflamed, and the sickest ones struggle to breathe. RSV is deadly on the other end of the age spectrum too, killing 6,000 to 10,000 elderly Americans every year.
For decades though, there was no way to stop the virus’s seasonal tide. The quest for a vaccine always came up short. And then suddenly, the vaccines started working.
This year, doctors have not just one but multiple new shots to prevent RSV. Three gained FDA approval in rapid succession in recent months: an antibody shot for infants called nirsevimab, a form of passive immunization for babies too young to get proper vaccines; a vaccine from Pfizer for both adults over 60 and pregnant mothers, who can pass the immunity on to their babies; and finally, a vaccine from GlaxoSmithKline also aimed at adults older than 60. Together, these herald a new era for RSV.
That these three new RSV shots are coming out at once is no coincidence. They succeed where others failed because they all target a specific weak spot in the virus, first identified in 2013. This strategy of finding a virus’s most vulnerable points applies to other pathogens too, and experts say it can revolutionize the design of vaccines for other diseases. In fact, it was quietly used to make the COVID vaccines from Pfizer and Moderna. Scientists had originally perfected the idea with RSV, only to repurpose it for the COVID vaccine, which raced ahead, given the urgency of the pandemic. This year, though, the shots are coming for RSV.
“We’re in a really good position, finally, after more than 65 years,” says Asunción Mejías, an infectious-diseases doctor at St. Jude Children’s Research Hospital.
The first attempts to make an RSV vaccine began not long after the virus’s discovery, in 1956, but an early trial ended so catastrophically that it had a chilling effect for decades.
It had started off with promise. The early vaccine was modeled after a successful one for polio, in which the virus is inactivated with a chemical called formalin. But when infants given the early RSV vaccine later caught the virus, a whopping 80 percent had to be hospitalized—compared with only 5 percent in the control group. Two of the babies died, their lungs ravaged. The vaccine did worse than offer no protection; it made the disease more severe. “It was such a disaster,” says Ann Falsey, an infectious-diseases doctor at the University of Rochester. Scientists spent years piecing together why—the vaccine riled up the wrong part of the immune system in very young babies—but they got no closer to making a vaccine that worked. The field was stuck.