Further efficacy studies on inactivated, aluminum-hydroxide-adsorbed vaccines against infectious coryza

Specific-pathogen-free chickens were given infectious coryza vaccines containing inactivated cells of Haemophilus paragallinarum adsorbed onto an aluminum-hydroxide gel. The vaccines were protective when given subcutaneously or intramuscularly but not when given intranasally. Vaccines prepared with two different commercial brands of aluminum-hydroxide gel gave similar protection. Vaccines in which the inactivating agent was thimerosal were more protective than similar vaccines in which the inactivating agent was formalin. Monovalent vaccines protected against challenge only from organisms of the same agglutination serovar, whereas bivalent vaccines protected against challenge from organisms of either serovar. A single dose of the vaccine, given at 16 weeks of age, was not as effective as two doses given at 12 and 16 weeks of age in protecting against challenge 12, 25, or 56 weeks after vaccination.