Table 2.

Protection provided by DNA vaccines against lethal homologous H5N1 challenge in mice unexposed and pre-exposed to H1N1 virus^§

Group	Subgroup (DNA vaccine)	Protection against H5N1 virus challenge (20LD50)
		Survival rate (survival number/total)	Body weight loss (% of the original)	Lung virus titers (log10TCID50/ml)
Unexposed to H1N1	NP DNA	4/11*	18.4 ± 1.02	9.93 ± 0.26
	M1 DNA	1/12	27.8 ± 2.86	10.25 ± 0.35
	NP+M1 DNAs	3/12	20.2 ± 0.54	8.96 ± 0.66
	Unimmunized	0/12	26.1 ± 1.76	10.85 ± 0.21
Pre-exposed to H1N1	NP DNA	10/12a, b	8.5 ± 2.01a, b	6.43 ± 0.84a, b
	M1 DNA	4/12	20.1 ± 2.63a,	10.05 ± 0.07
	NP+M1 DNAs	12/12a, b	7.9 ± 0.72a, b	7.12 ± 0.17a, b
	Unimmunized	4/12a	17.8 ± 1.29a	9.78 ± 1.39

^§Mice were randomized into two groups. One group was infected with H1N1 virus, and the other was uninfected. Six weeks later, mice in each group were randomly divided into 4 subgroups. Three subgroups were immunized with a single dose of NP DNA, M1 DNA and NP+M1 DNAs, respectively, and the rest remained unimmunized as a control. Six weeks after immunization, all the mice were challenged with a lethal dose (20LD₅₀) of H5N1 virus. Lung virus titers, body weight losses and survival rates of mice were determined 3 days, 7 days and 21 days post-challenge, respectively.

^aSignificant difference (p < 0.05), compared with the corresponding unexposed mice.

^bSignificant difference (p < 0.05), compared with the pre-exposed but unimmunized control.

*One mouse in the group died during anesthesia.