ranjan

When a virus is widely circulating in a population and causing many infections, the likelihood of the virus mutating increases. The more opportunities a virus has to spread, the more it replicates, and the more opportunities it has to undergo changes.   Immune system is a complex network of cells, tissues and organs. They help together the body to fight infections and other diseases. When germs such as bacteria or viruses invade the body, they attack and multiply. This is called an infection. This infection causes the disease that makes the person sick. The immune system protects one from the disease by fighting off the germs.  The immune system defends the body against substances it sees as harmful or foreign. These substances are called antigens. They may be germs such as bacteria and viruses, chemicals or toxins. They could also be cells that are damaged from things like cancer or sunburn. When immune recognizes an antigen, it attacks it which is called immune response. Part of this