Anti N1 Cross-Protecting Antibodies Against H5N1 Detected in H1N1 Infected People

The A(H5N1) influenza virus pandemic may be the result of avian H5N1 adapting to humans, leading to massive human to human transmission in a context of a lack of pre-existing immunity. As A(H1N1) and A(H5N1) share the same neuraminidase subtype, anti-N1 antibodies subsequent to H1N1 infections or vaccinations may confer some protection against A(H5N1). We analysed, by microneutralization assay, the A/Vietnam/1194/04 (H5N1) anti-N1 cross-protection acquired either during A/NewCaledonia/20/99 (H1N1) infection or vaccination. In cases with documented H1N1 infection, H5N1 cross-protection could be observed only in patients born between 1930 and 1950. No such protection was detected in the sera of vaccinated individuals.