Experimental Vaccination of Chickens Against Avian Influenza Subtype H5 with an Inactivated Oil Emulsion Vaccine

Abstract

Doses of 500, 125 or 62.5 μl of two inactivated influenza vaccines prepared using the virulent A/tern/S. Africa/61 (H5N2) strain were injected subcutaneously into five week old SPF chicks.

HI antibody appeared faster but also waned faster after vaccination with vaccine A, in aqueous solution, than with the oil emulsion based vaccine B. This was associated with a slightly better protection against challenge with the virulent live virus by vaccine A 3 weeks after vaccination. Challenge was not followed by a significant increase of HI titres or appearance of precipitating antibody. Virus titres were approximately the same in faecal samples from all vaccinated groups and from a non-vaccinated control group at the third day after challenge.

Birds had higher mean HI titres 11 weeks after vaccination with vaccine B than with vaccine A, and were better protected against challenge. An increase in HI titres and the appearance of precipitating antibody was observed after challenge of the less well protected groups vaccinated with 500 or 125 μl of vaccine A.

While most birds that died or became sick had no circulating antibody at the time of challenge, some had titres of 3, 4 or 5. However, many vaccinated birds without circulating antibody overcame challenge without developing symptoms.