$(a)$ State the principle of immunisation. Name two diseases for which vaccines are available.
$(b)$ Mention two basic principles of prevention of infectious diseases.

(N/A) The principle of immunisation is based on the property of the immune system to develop memory against a specific microbe. When a vaccine (a weakened or dead microbe) is introduced into the body,the immune system recognizes it as foreign,produces antibodies,and creates memory cells. This allows the body to fight off the actual pathogen effectively if exposed in the future.
Examples of diseases for which vaccines are available: $Polio$,$Tetanus$.
$(b)$ The two basic principles of prevention of infectious diseases are:
$(i)$ General ways of prevention: This involves maintaining personal and public hygiene,such as keeping surroundings clean,ensuring safe drinking water,and proper waste disposal to prevent the spread of pathogens.
$(ii)$ Specific ways of prevention: This involves strengthening the immune system through proper nutrition and the use of vaccines to provide specific immunity against particular infectious agents.