An RSV shot was 82.6 percent effective in older adults

Structural biologists at the NIH eventually found why: the virus's surface protein flips shape once it infects a cell, and earlier vaccines had targeted the wrong shape. Researchers used the corrected, pre-infection shape of that protein to build a new vaccine tested in adults 60 and older.

In a trial of nearly 25,000 adults, the vaccine, built around the stabilized prefusion form of the RSV surface protein, was 82.6 percent effective at preventing RSV-related lower respiratory tract disease compared with placebo, in a population where RSV had long been underappreciated as a cause of serious illness.

The vaccine was approved in 2023 as the first RSV vaccine for older adults, decades after the original failed pediatric attempt had nearly stalled RSV vaccine research altogether. Protection appears to wane somewhat by the second and third seasons after vaccination, and researchers are still studying how often a booster dose might be needed.

A decades-old vaccine failure finally found its fix.