[Perspective] First flu is forever

Influenza is a threat that has been with humans throughout history, fueled by a constant race between host immunity and viral evolution. Control strategies rely on annual immunizations and require frequent updates of the vaccine, an expensive, cumbersome, and not always foolproof process. Efforts are therefore under way to develop vaccines that confer broadly cross-protective immunity to diverse influenza strains. Cross-immunity is pervasive in nature; in multistrain viral diseases such as influ