Protection of chickens against challenge with virulent influenza A viruses of Hav5 subtype conferred by prior infection with influenza A viruses of Hsw1 subtype.

Prior infection of six-week-old chickens with influenza A viruses of Hsw1 haemagglutinin subtype and irrelevant neuraminidase subtypes reduced the deaths and sickness in groups of those birds challenged with A/tern/s. Africa/61 (Hav5Nav2/3) and A/chicken/Scotland/59 (Hav5N1).