Rabies-specific IgG, IgA, and IgM Ab responses to immunization with rabies vaccine in naive and immune volunteers. The naive volunteers (left) were immunized at days 0, 28, and 56, and the concentration of rabies-specific IgG- (A), IgA- (B), and IgM-specific Ab (C) concentration was measured at various days after the first and third doses of immunization. The immune volunteers (right) were immunized at day 0, and the frequencies of rabies IgG- (D), IgA- (E), and IgM-specific (F) Ab were measured at various days after immunization. The horizontal bars represent the geometric mean concentration at each time point. The broken line represents the World Health Organization IgG seroconversion level of 0.5 IU/mL. The magnitude of the IgG Ab response after booster immunization in the immune group was greater than after primary, secondary, and tertiary immunization in the naive group.