Unlike current FDA-approved flu treatments, which target viral enzymes and can quickly become useless as the virus mutates, this therapy did not allow viral escape, even after a month of repeated exposure in animals. That difference could prove crucial in future outbreaks, when survival often depends on how quickly and effectively doctors can deploy treatments and vaccine development will take about six months.

“This is the first time we’ve seen such broad and lasting protection against flu in a living system,” said Silke Paust, an immunologist at JAX and senior author of the study. “Even when we gave the therapy days after infection, most of the treated mice survived.”

The insights challenge a long-held belief that for antibodies to be useful as a therapy against viruses, they must be “neutralizing” antibodies that bind directly to viruses and block them from infecting cells. Instead, the team engineered “non-neutralizing” antibodies, which don’t prevent infection but tag infected lung cells and recruit the body’s immune system to clear the infection. This new approach could reshape how scientists design treatments for other viruses.