Why would my child need multiple injections of the same vaccines?

Various reasons: -sometimes body must be challenged multiple times to build immunity. 1 dose of vaccine not enough to stimulate long antibody protection -immune memory fades over time. Boosters remind the immune system to be vigilant about dangerous whooping cough, tetanus, & such infections -1st dose may not stimulate immune response in some and the 2nd dose catches those “non-responders” example mmr.

Biological learning: The ability of the body to develop resistance to germs from a vaccine is directly to the maturity of the immune system. In the first months after birth, moms transfered immunity (placental)interferes with babies ability to make antibodies but they are very vulnerable so repeated vaccines are needed. As they get past 5y or so, kids can hold on to the stimulation for many years like an adult.