A vaccination strategy that can protect against multiple strains of influenza virus is described in a report published this week in Nature Immunology.

Influenza viruses can rapidly mutate, which allows outgrowth of strains that are not recognized by antibodies elicited by current vaccines. Thus every flu season requires vaccination against the prevalent circulating influenza viruses, though newly emerging strains may not be represented in vaccine formulation and therefore pose a potential gap in immune protection.

Maureen McGargill and colleagues find that mice immunized against the H3N2 influenza virus in the presence of rapamycin, a drug that targets the host enzyme mTOR, could elicit protective immunity to the mice when subsequently challenged with H1N1, H5N1 or the newly emergent H7N9 influenza strains. Rapamycin inhibits the generation of high-affinity antibodies against the H3N2 virus, instead eliciting immune memory and antibody responses against conserved viral sequences. Thus, using rapamycin to dampen the immune response during vaccination paradoxically improves protection against a broader range of influenza strains.