Structural Basis of Preexisting Immunity to the 2009 H1N1 Pandemic Influenza Virus

Abstract

Swine Flu Neutralized The 2009 H1N1 flu virus had an unusually low infection rate in elderly people. An antibody isolated from survivors of the 1918 flu pandemic was recently shown to cross-neutralize 2009 H1N1 viruses. Xu et al. (p. 357 , published online 25 March) report crystal structures of the virus envelope protein, hemagglutinin (HA) from 2009 H1N1 and of 1918 H1 HA in complex with a neutralizing antibody that cross-reacts with both pandemic viruses. These studies reveal an epitope that is conserved in the pandemic viruses, but divergent in other known H1 HAs, from the 1930s to the present. This antigenic similarity explains the age-related immunity to the 2009 H1N1 influenza.