Antibody responses induced by Japanese whole inactivated vaccines against equine influenza virus (H3N8) belonging to Florida sublineage clade2.

In 2010, the World Organisation for Animal Health recommended the inclusion of a Florida sublineage clade2 strain of equine influenza virus (H3N8), which is represented by A/equine/Richmond/1/07 (Richmond07), in equine influenza vaccines. Here, we evaluate the antigenic differences between Japanese vaccine strains and Richmond07 by performing hemagglutination inhibition (HI) assays. Ferret antiserum raised to A/equine/La Plata/93 (La Plata93), which is a Japanese vaccine strain, reacted with Richmond07 at a similar titer to La Plata93. Moreover, two hundred racehorses exhibited similar geometric mean HI antibody titers against La Plata93 and Richmond07 (73.1 and 80.8, respectively). Therefore, we can expect the antibody induced by the current Japanese vaccines to provide some protection against Richmond07-like viruses.