Sustained immunity (memory)
memory B-cells remain sensitized to the specific antigen to which they were originally exposed. on re-exposure, the memory cells rapidly respond.
First, they divide and form new sensitized blast cells and new sensitized plasma cells.
blast cells continue to divide producing many more sensitized plasma cells. and then it can rapidly make large amounts of antibody specific for the sensitizing antigen.
Because pf memory cells, we do not worry even upon multiple re-exposure because the anamnestic (immune) response tp the antigen.