Antibody response to DNA vaccine against H5N1 avian influenza virus in broilers immunized according to three schedules.

Broiler type chickens were immunized intramuscularly with a DNA vaccine encoding hemagglutinin (HA) from H5N1 avian influenza virus. The chickens were divided into four groups: control group which was not immunized, a group which obtained only one dose, and two groups which were immunized twice, one group with a boost two weeks after the priming and the other four weeks. Blood samples were collected at several time points and the dynamics of the humoral response to the vaccine was studied. High level of anti-HA antibodies was detected only in the last two groups, that is in chickens immunized according to the prime-boost strategy, regardless of the schedule. An additional interesting observation of this study was detection of the cross-reactivity of an anti-H5 HA positive serum with H5N2 and H1N1 viruses, suggesting that the DNA vaccine tested can induce antibodies of a broad specificity.