Define vaccine. Who coined the term ?

Explanation

### Step-by-Step Text Solution:

1. **Definition of Vaccine**:
A vaccine is a biological preparation that provides active acquired immunity to a particular infectious disease. It typically contains killed or attenuated (weakened) forms of the germs (pathogens) that cause the disease. When introduced into the body, these components stimulate the immune system to recognize and fight the pathogens without causing the disease itself.

2. **Mechanism of Action**:
Vaccines work by mimicking the presence of the disease-causing organism. They contain antigens that trigger the immune response, leading to the production of antibodies. This process helps the immune system "remember" the pathogen, so if the body is exposed to the actual pathogen in the future, it can respond more quickly and effectively.

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