Question

thanks but memory cells remember the disease which has affected our body once and they prevent the microorganism of that disease spreading twice in our body. so chikenpox should not happen twice but still it does.why?

Answer 1

We develop antibodies to the infection first-time round, and become immune to catching it again. But it can happen if our immune system or the first infection was very low then it can arise for a second time because the virus rest in human body in dormant state.