Describe how vaccines can help the body's natural defenses against viruses?
Vaccines work by improving the natural defensive systems of the body. Our immune system is capable of remembering an attack on our body by pathogens (harmful microorganisms) and vaccines make use of this fact.
Vaccines are, typically, dead, weakened or inactive viruses or other pathogens, which on entry to our body alert the immune system. The lymphocytes (T cells and B cells), under the impression that an actual full-scale attack has taken place on our body, spring into action and rapidly kill this infection. Some of these cells are converted to memory cells and the immune system remembers this type of infection so that in the future, when encountered, such infections can be more rapidly dealt with. This acquired immunity helps keep our bodies healthy. In older times, the lack of vaccines meant that the body had to develop its natural immunity against an infection, which was time consuming and slower as compared to the growth rate of infectious microorganisms leading to high mortality rates.