Figure 4. Mutated viruses are less toxic to mice than wild type of A/PR8.

A. Body weight changes of C57/B6 mice inoculated with Pol1, Pol2, A/PR8 or mock infected. Body weight was monitored daily. B. Lungs’ viral titers in C57/B5 mice inoculated with different viruses. Five mice in each group were sacrificed on day 3 and 6 post vaccination. Lungs were homogenized in PBS to make 10% (wt/vol) (lungs) tissue homogenates, and viral titers were determined by TCID₅₀ assay. Data were analyzed on day 6 after vaccination. P<0.05