Lack of cross-immune reactivity against influenza H5N1 from seasonal influenza vaccine in humans.

In a small pilot study, sera from 10 healthy human volunteers were taken pre-vaccine, then 1, 3, and 6 months post-seasonal influenza immunization (using the 2005/2006 Northern hemisphere vaccine: A/New Caledonia/20/99(H1N1)-like, A/California/7/2004(H3N2)-like, and B/Shanghai/361/2002-like strains). Eight out of 10 subjects demonstrated satisfactory HAI titers (> or = 40) after seasonal influenza vaccination between 1 and 6 months post-vaccine. These sera were then tested for inhibitory activity against A/HK/483/97 and A/Thailand/1(KAN-1)/04 H5N1 influenza viruses using standard hemagglutination inhibition and microneutralization assays. In contrast to several other studies in both humans and animals on the cross-immunity between different influenza A viruses, antibodies produced to the influenza A(H1N1) component of the seasonal influenza vaccine showed no cross-reactivity to these avian influenza A(H5N1) viruses. Possible reasons for this contrasting result are discussed. 2008 Wiley-Liss, Inc.