Class 12 Biology Notes

Class 12 Biology Notes - Vaccines

A vaccine is an inactivated form of bacteria or virus that is injected into the body to simulate an actual infection. Since the injected microorganisms are ‘dead,’ they don’t cause a person to become sick. Instead, vaccines stimulate an immune response by the body that will fight off that type of illness.

Vaccines can be prophylactic/preventive (example – to prevent or ameliorate/amend the effects of a future infection by a natural or “wild” pathogen), or therapeutic (that treats the disease for example – vaccines against cancer are being investigated).

How the Immune System Works?

To better understand vaccines, we need to know more about how our body’s immune system works. There are special cells in our bloodstream called white blood cells. They have the very important job of fighting off foreign invaders such as viruses and bacteria. These invaders are known as antigens. White blood cells are like the armed forces of our body. They are constantly on the lookout for antigens that have entered our body, compromising our health.

We also have a group of defensive proteins circulating in our blood that are known as antibodies. They float around in non-active form until triggered by an immune response, such as the detection of an antigen. When the antigen/or any foreign substance reaches our body, billions of additional antibodies are produced that will fight off that particular antigen. This enormous army of antibodies now joins in the attack with the white blood cells and kills the germs or any agent that has entered our body.

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