Background: Infection with pandemic H1N1 influenza A viruses (IAVs) containing hemagglutinin (HA) proteins with globular heads that differ substantially from seasonal strains results in a boost in broadly cross-reactive antibodies that bind to the HA stalk. Boosting these antibodies has become an attractive strategy for creating a universal IAV vaccine. Therefore, it was essential to determine whether vaccines containing H1N1 viruses whose head domains differ substantially compared to seasonal strains could also achieve this boost.
Methods: Prospective samples of subjects who had received the A/New Jersey/1976 (NJ/76) vaccine and healthy, age-matched controls were assessed for the presence of anti-HA stalk antibodies before and after receiving the A/California/04/2009 (Cal/09) vaccine between October 2009 and January 2010.
Results: Individuals who received either the NJ/76 vaccine or the Cal/09 vaccine experienced a robust boost in HA stalk-reactive, neutralizing antibodies similar to what has been observed in individuals infected with Cal/09.
Conclusions: These results demonstrate that vaccines containing viruses whose HA head domains that differ substantially from seasonal strains are capable of boosting titers of HA stalk antibodies. Furthermore, anti-HA stalk antibodies elicited by vaccination appear to be long-lived and therefore could be targeted for the generation of a universal IAV vaccine.