1. Highly pathogenic avian influenza (HPAI) A(H7N3) viruses have continued to circulate in Mexican poultry since their initial identification in the summer of 2012. Although several control strategies have been implemented, the virus has spread to several states, causing enormous economic losses in the commercial poultry sector. Important factors to ensure vaccine potency include a close match between the antigen and circulating strains and using sufficient antigen to protect the birds and prevent shedding during subsequent infections.

2. The following study investigated the haemagglutin (HA) concentration of an adjuvanted vaccine produced from a reverse genetics-modified low-pathogenic avian influenza A(H7N3) virus that could protect chickens against homologous challenge. Inactivated vaccine formulations with different HA concentrations (0.8, 1.1, 1.3 and 3.1?μg/0.5?ml haemagglutinin) were prepared and tested in chickens.

3. The results showed that the formulations containing 1.1?μg or more of HA per 0.5?ml dose protected the birds against disease symptoms and reduced viral replication when compared with the vaccine containing 0.8?μg/0.5?ml.