Every year brings new variations of flu as well as a new race to develop vaccines against them. Those efforts might get a boost from a new report in Science Translational Medicine (2013, DOI: 10.1126/scitranslmed.3005996). The work reveals how placement of sugar chains on the virus controls the immune response to flu. The flu protein hemagglutinin helps bind flu virus to cells, and flu frequently evolves by switching the amino acid sites of glycosylation on this protein. Adolfo García-Sastre of the Icahn School of Medicine at Mount Sinai and Rafael A. Medina of Pontifical Catholic University of Chile led a team that altered or removed those sugar-bedecked sites. They tested the resulting viruses’ effects on mice and on human blood serum. Their results confirm researchers’ hunch that carbohydrate chains help flu virus evade preexisting antibodies. The work also shows that sugar chain placement influences the new antibodies the body churns out after infection. Specifically, it determines how broad a range of flu viruses those antibodies will work against. Controlling glycosylation sites within a vaccine, the authors suggest, could likewise tune the vaccine’s effectiveness.