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Asterisk denote the level of significance (*, P<0.05; **, P<0.01; ***, P<0.001 and ****, P<0.0001. Responder frequency (R/F) was calculated as four-fold rise of antibody titer compared to day 0 and cumulative responder frequency (CRF) calculated from either four-fold increase in any day post immunization (day 14 and day 28).
