Evaluation of inactivated infectious coryza vaccines in chickens challenged by serovar B strains of Haemophilus paragallinarum.

Four monovalent experimental vaccines (VI, V2, V3 and V7) containing an Argentinean serovar B strain (H8) of Haemophilus paragallinarum and three different commercial vaccines, either bivalent (V4 and V5) containing serovars A and C, or trivalent (V6) containing serovars A, B and C were administered by subcutaneous or intramuscular routes as a single or double dose (at 3-week intervals) to chickens of between 6 and 10 weeks. Three to 7 weeks after the last vaccination, vaccinated and non-vaccinated chickens were challenged by intrasinus inoculation with Argentinean serovar B strains of H. paragallinarum. When the vaccinated chickens were exposed to a severe challenge with the vaccinal strain (H8) some experimental vaccines protected, whereas all commercial vaccines failed to protect. The experimental vaccines manufactured in broth (V2, V3 and V7) protected more effectively than the vaccine produced in chicken embryos (VI). Failure of the commercial trivalent vaccine V6 to protect may be related to the method of manufacture. Vaccine V7 protected against challenge from either the vaccinal strain (H8) or three Argentinean serovar B strains (H6, Hll and HI2). These results confirm the necessity of including serovar B regional strains in the formulation of local vaccines.