TABLE 2.
Protective efficacy of influenza H9N2 inactivated vaccines against infection with HK/1073 and Ck/G9 viruses
| Vaccine groupa | HI antibody titerb
|
Protection against challengec
|
||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| HK/1073
|
Ck/G9
|
|||||||||
| Mean virus titerd
|
No. protectede/total no.
|
Mean virus titer
|
No. protectede/total no.
|
|||||||
| HK/1073 | Ck/G9 | Lung | Nose | Lung | Nose | Lung | Nose | Lung | Nose | |
| Vaccinated mice | ||||||||||
| HK/1073 | 91 | 40 | ≤1.2 | 0.9 ± 0.2 | 7/7 | 6/7 | 1.8 ± 1.6 | 1.1 ± 0.7 | 7/8 | 5/8 |
| HK/1073 + alum | 564 | 62 | ≤1.2 | ≤0.8 | 7/7 | 7/7 | ≤1.2 | ≤0.8 | 8/8 | 8/8 |
| Ck/G9 | 10 | 219 | 3.5 ± 1.5f | 2.4 ± 1.2g | 1/7 | 1/7 | ≤1.2 | 0.9 ± 0.2 | 8/8 | 7/8 |
| Ck/G9 + alum | 12 | 2,560 | 1.5 ± 0.5 | 1.2 ± 0.4 | 5/7 | 3/7 | ≤1.2 | ≤0.8 | 8/8 | 8/8 |
| Alum | 10 | 10 | 7.5 ± 0.7 | 2.9 ± 0.8 | 0/7 | 0/7 | 5.9 ± 1.1 | 1.9 ± 0.4 | 0/8 | 0/8 |
| Infected mice | ||||||||||
| HK/1073 | 103 | 13 | ≤1.2 | ≤0.8 | 7/7 | 7/7 | ≤1.2 | ≤0.8 | 8/8 | 8/8 |
Groups of 6-week-old female BALB/c mice (n = 20) were injected i.m. with 1 dose of 10 μg of formalin-inactivated vaccine alone, vaccine with 1% alum, or alum alone or were infected i.n. with 106 EID50 of HK/1073 virus as a positive control.
Serum samples were collected 3 months after vaccination or infection and tested by HI assay against HK/1073 and Ck/G9 viruses. HI titers are expressed as the geometric mean titer of 10 mice per group.
Mice were challenged i.n. 3 months later with 100 50% mouse infectious doses of HK/1073 (105.5 EID50) or Ck/G9 (106.3 EID50) virus. Virus titers and protection from infection were determined on day 3 p.i. Virus titers were calculated by the method of Reed and Muench (29) and are expressed as the mean log10 EID50/ml ± the standard deviation of seven or eight mice per group.
With one exception (footnote g), mice administrated H9N2 vaccine either with or without alum had significant reductions in lung and nasal virus titers compared with mice that received alum alone following challenge with either HK/1073 or Ck/G9 virus (P < 0.05).
Mice were considered protected if no virus was detectable in 0.2 ml of a 1:10 dilution of lung homogenate (virus titer, ≤101.2) or a 1:2 dilution of nasal passage tissue homogenate (virus titer, ≤100.8).
Viral titer was significantly higher than lung titer for mice that received HK/1073 vaccine alone (P < 0.01).
Viral titer was not significantly different from that for mice administered alum alone.