Efficacy of a trivalent Haemophilus paragallinarum vaccine compared to bivalent vaccines

The efficacy of a trivalent oil-adjuvant Coryza vaccine containing serotypes A, B and C of Haemophilus paragallinarum has been compared with that of a bivalent oil-adjuvant Coryza vaccine containing serotypes A and C and that of a commercially available, bivalent A1(OH)3-potentiated vaccine, containing types A and C. The trivalent vaccine, given at 10 and 17 weeks of age, provided the best protection. Even at 55 weeks after booster vaccination, chickens were still significantly protected, following severe challenge with either of the three serotypes of Haemophilus paragallinarum. Both bivalent vaccines did not protect against type B challenge. Furthermore the oil-adjuvant vaccines induced higher HI-A titers, which correlate with protection, compared to the A1(OH)3-potentiated vaccine. The results show that type B strains are pathogenic and constitute a distinct immunotype and thus a Coryza vaccine should contain three serotypes to obtain a broader protection against all serotypes.