Interestingly, a recent study by Andrews et al., Sci. Immunol. 2, eaan2676 (2017), suggests that cross-reactive group 1/group 2 HA stem antibodies may be more likely to be elicited in humans by a ...

Hemagglutinin is one of two critical flu virus surface proteins. And it isn't even the entire protein that interests flu scientists, but the protein's "stem" region, which has long been a key target.