If animals or humans become sick with an infectious bacterial disease and then recover, the type of bacteria that caused the disease does not usually make them sick again. What is the reason for this?
Answers
Answer:
the immune system memorises the bacteria and then just make the anti-bodies to fight with the virus and hence we don't fell sick again and again by the same virus
Let me explain to you in a very simple way (just for you to grasp the basic concept)-
The first time you get sick with an infectious bacterial disease and then recover, your immune system 'recognises' the pathogen. That particular pathogen gets 'registered' and your immune system produces antibodies to fight that infection. Now your immune system is prepared, and you are less likely to catch the disease a second time, and even if you do, you'll recover easily. This is the basic concept of 'vaccination'.
Now to answer your question in more 'technical terms', I've provided you with an excerpt from Wikipedia-
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 threat, destroy it, and to further recognize and destroy any of the microorganisms associated with that agent that it may encounter in the future.