Research brief

Abstract

Although the 2009 H1N1 pandemic influenza virus has caused about 17 000 deaths worldwide so far, the death toll in elderly people has been unexpectedly low. Now, two studies explain why elderly people have some pre-existing immunity to 2009 H1N1. The first study shows that the crystal structure of the haemagglutinin of the A/California/04/2009 H1N1 virus is very similar to that of the haemagglutinin of early 20th century human H1N1 viruses, particularly near the receptor binding domain. The second study shows that vaccination with the 1918 H1N1 pandemic influenza virus protects mice against the 2009 H1N1 virus and vice versa, and that antibodies that neutralise the pandemic strains are directed against a region of the haemagglutinin receptor binding domain that is highly conserved in the 1918 and 2009 viruses. Finally, both studies note that although this conserved region is glycosylated in seasonal H1N1 influenza strains, it is unglycosylated in both pandemic strains, which makes the region susceptible to antibody neutralisation. These results suggest ways to design vaccines to protect against similar future pandemic influenza viruses and to limit the transformation of 2009 H1N1 into seasonal influenza.