Haemagglutinin dose and protection against HPAI A(H7N3) in birds
Although vaccination against avian influenza has been implemented in Mexico, outbreaks of highly pathogenic avian influenza (HPAI) have continued to occur in poultry, leading to substantial economic losses. These persistent outbreaks raised concerns regarding the protective efficacy of existing vaccines and whether the administered antigen doses were optimal for effective virus control.
A study published in British Poultry Science evaluated the haemagglutinin (HA) concentration required in inactivated vaccines to protect chickens against HPAI A(H7N3) virus and to reduce viral replication and shedding.
The study assessed vaccine formulations containing varying HA concentrations (0.8, 1.1, 1.3, and 3.1 μg/0.5 ml) in specific pathogen-free chickens. Vaccines containing ≥1.1 μg HA per 0.5 ml dose effectively protected birds from clinical disease and significantly decreased viral replication compared to lower-dose formulations. These findings indicate that an HA dose of at least 1.1 μg is required to provide sufficient protection and to control viral shedding.
The effectiveness of a preventive program based, among other factors, on poultry vaccination depends on adherence to professional standards, including vaccine suitability and quality. Vaccine failure to prevent disease does not inherently imply a conceptual deficiency but warrants comprehensive evaluation of vaccine quality and administration.
