CBSE & NCERT Solutions for class 12 biology Vaccines
Biology Class 12: A vaccine is a biological preparation that provides active acquired immunity (Active immunity refers to the process of exposing the body to an antigen to generate an adaptive immune response – the response takes days/weeks to develop but may be long-lasting—even lifelong. Active immunity is usually classified as natural or acquired). A vaccine typically contains an agent that resembles a disease-causing microorganism and is often made from weakened or killed forms of the microbe, its toxins, or one of its surface proteins. The agent stimulates the body’s immune system to recognize the agent as a foreign substance, thus the body’s defense system fights with it, destroys it, and recognize and destroy any of these microorganisms that it later encounters.
Or we can define vaccine as-
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).
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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 a 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.
For example, imagine that an influenza virus has entered the body and has begun replicating. The white blood cells patrolling the bloodstream have spotted these antigens. They gather their troops, produce a few billion antibodies geared to fight this specific virus, and launch a massive attack.
It will take some time for the body to completely fight off these germs, and that’s why a person develops symptoms of the illness for a short time. However, if a person has a healthy and strong immune system, he will take a short time to recover. In this way, the body has developed a very strong army of antibodies for that particular agent (virus/ bacteria). They remain on the lookout for that same antigen to invade. The next time if it enters the body, it will be overtaken by the immune response so fast that there won’t be any symptoms.
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