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Microscopic agglutinating test. Serum antibody titer to strain 203 was measured at the given time points postvaccination and postinfectious challenge (PI, shaded bars). Group means (n = 6) + standard error of the mean (SEM). An asterisk (*) indicates statistical difference from week 0 within vaccine group and statistical difference between vaccine groups and control group within a time point (week); P ≤ 0.05.
