Protective efficacy of DNA vaccine encoding codon-optimized HA gene of H5 subtype avian influenza virus A/Duck/Anhui/1/2006(Clade 2.3)

To evaluate the efficacy of DNA vaccine pCAGGoAHHA, which encodes the hemagglutinin (HA) protein from isolate A/Duck/Anhui/1/2006(H5N1) [DKAH/1/06(H5N1)]of waterfowl clade, groups of 3-week-old specific pathogen free (SPF) chickens were intramuscularly injected with 5 μg, 10 μg, 20 μg, 50 μg and 100 μg of the DNA vaccines, respectively, boosted with the same dosage after three weeks. All chickens were nasally challenged with 106 EID50 of highly pathogenic avian influenza virus (HPAIV) A/Duck/Fujian/31/2007 (H5N1) [DKFJ/31/07 (H5N1)] at two weeks after the boost. Oropharyngeal and cloacal swabs were collected from all groups at 3, 5 and 7 days post the challenge for isolation of virus in embryo eggs, and the sera were collected after vaccination and challenge to measure the titers of antibodies by hemagglutinin inhibition (HI) and neutralization (NT) tests. Results shown that a complete protection was achieved in groups with a doses as low as 20 μg of the DNA vaccine,without any clinic signs, death and virus shedding. However, partial protection of 25 % and 75 % was provided in 5 μg and 10 μg of dosage groups, respectively. Our results indicated that pCAGGoAHHA were able to induce highly protective efficacy and could be a potential H5N1 candidate vaccine against the H5 Subtype HPAIV.