Waning immunity
Waning immunity describes the loss of protective antibodies over time. Infections and vaccines induce an immune reaction, part of which is a memory function, mostly contained in Memory B-Cells. When reexposed to the antigen in question, the B-Cells begin to reproduce and make antibodies to the antigen. In some cases, the memory function is more effective than in others. For instance, the tetanus vaccine's effectiveness wanes over time. The same effect has also been noted with the pertussis vaccine (whooping cough). Though adults contracting pertussis' flu-like symptoms and persistent cough are in little danger, children yet to be immunized can catch it from those adults so exposed and therein the danger lies as whooping cough in an infant can quickly drain a child of its reserves and death can ensue. Currently there is a newer tetanus/pertussis/diphtheria vaccine used when adults require a tetanus booster.[1] Immunity to chickenpox acquired via natural infection probably lasts a lifetime, however this is less clear, as the virus persists in nerve roots indefinitely which may help maintain an immune response.
