What are vacines ?give examples.
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A vaccine is a biological preparation that provides active acquired immunity to a particular disease.
A vaccine typically contains an agent that resembles a disease-causing
micro-organism 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 threat, destroy it, and keep a record of
it, so that the immune system can more easily recognize and destroy any
of these micro-organisms that it later encounters. Vaccines can be prophylactic (example: to prevent or ameliorate the effects of a future infection by any natural or "wild" pathogen), or therapeutic (e.g., vaccines against cancer are also being investigated).
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