Single amino acid substitutions in the hemagglutinin of influenza A/Singapore/21/04 (H3N2) increase virus growth in embryonated chicken eggs.

Most of the recently circulating H3N2 influenza A strains do not replicate well in embryonated chicken eggs and had to be isolated by cell culture, which presents a great challenge for influenza vaccine production using embryonated chicken eggs. We previously reported that a human H3N2 virus, A/Fujian/411/02, which replicates poorly in eggs, could be improved by changing a minimum of two HA residues (G186V/V226I or H183L/V226A). Here, we extended our work to the A/Singapore/21/04 strain that was also unable to grow in eggs. We showed that a single amino acid substitution of either G186V or A196T in the HA resulted in significantly increased virus replication in eggs without affecting virus antigenicity.