Genetic characterization of an H5N1 avian influenza virus from a vaccinated duck flock in Vietnam.

This study reports the genetic characterization of a highly pathogenic avian influenza virus subtype H5N1 isolated from a moribund domestic duck in central Vietnam during 2012. In the moribund duck's flock, within 6 days after vaccination with a commercial H5N1 vaccine (Re-5) to 59-day-old birds, 120 out of 2,000 ducks died. Genetic analysis revealed a substantial number of mutations in the HA gene of the isolate in comparison with the vaccine strains, Re-1 and Re-5.