FIG. 3.
Differences in percentages of anti-PR8 IgG production in serum (A) and survival rates (B) based on the period between oral immunization and nasal infection or on the quantity of immunogen. Nine-week-old female BALB/c mice were immunized with a single dose of 105.9 EID50 and with two doses of 104.9 EID50 of PR8 at various weeks and at 6 and 2 weeks before nasal inoculation (103.5 EID50 of PR8), respectively. The anti-PR8 IgG titer in serum was measured just before nasal inoculation of PR8. The survival rates were observed for 14 days after nasal inoculation of PR8.