A new antibody treatment combines two antibodies to improve protection against RSV. Unlike existing therapies, RSV did not develop resistance to the combination even after 20 consecutive treatments.

Respiratory syncytial virus, better known as RSV, is one of the leading causes of hospitalization in infants. It also causes serious lung infections in older adults and people with weakened immune systems. Current measures reduce severe disease, but RSV can evolve to escape them.

Unlike current RSV therapies, which rely on a single antibody, the new treatment attacks the virus from two different locations. One antibody binds near the top of the viral fusion protein, while the other attaches closer to its center. Together, they lock the protein into a shape that prevents RSV from infecting human cells.

The antibodies recognize parts of the virus that have remained largely unchanged across circulating RSV strains. By targeting two conserved regions instead of one, the treatment is designed to remain effective even as the virus continues to evolve.

Protection Length and Breadth

The antibody combination neutralized both major RSV groups, RSV A and RSV B. It also remained effective against dozens of naturally occurring viral variants collected from around the world, showing that the antibodies recognize parts of the virus that rarely change.

Both antibodies were engineered to remain in the bloodstream longer after injection, potentially allowing a single dose to provide protection throughout an RSV season and reducing the number of injections needed for newborns and other high-risk patients. In animal studies, the engineered antibodies remained in circulation substantially longer than their unmodified counterparts while maintaining their antiviral activity.

The antibody combination performed well in both mice and rats. Animals receiving the treatment showed markedly lower virus levels in both the lungs and upper airways after exposure to RSV.

The cocktail also remained effective against viral variants known to evade single-antibody treatments, demonstrating that combining two antibodies can overcome resistance that defeats either one alone. In some experiments, virus levels in the lungs fell by nearly 300-fold compared with untreated animals. Similar reductions were observed across infections caused by both RSV A and RSV B, supporting broad antiviral activity.

The principle behind the development of this antibody cocktail may extend well beyond RSV. Similar challenges have emerged for influenza, SARS-CoV-2, and other rapidly changing viruses. Combining antibodies that recognize different conserved regions of a virus may provide a way to stay ahead of that evolution.

Similar strategies are already gaining momentum in other areas of medicine. Bispecific antibodies, or engineered antibodies designed to bind two different targets simultaneously, are now approved or under investigation for several cancers and immune disorders. Multi-antibody therapies have also become an important strategy for treating rapidly evolving viruses.

Future antiviral therapies may increasingly focus not only on how powerfully they neutralize a virus today, but also on how well they withstand viral evolution years from now. By attacking multiple conserved targets at once, antibody combinations may offer a more durable approach to preventing infection while helping preserve the effectiveness of these treatments as viruses continue to evolve.