Vaccination is a simple, safe and effective way of protecting people against harmful disease before they come into contact with them.A vaccine is either a cell suspension or a by-product excreted by the cell.
A vaccine trains our immune system to produce antibodies (protein that fight disease).
Immunization is a process by which a person becomes protected against a disease through vaccination.
Vaccines contain a microorganism or virus in a weakened, live or killed state, or proteins or toxins from the organism.
 Vaccines do not cause the disease or put you at risk of its complications. ❖ Most vaccines are given by an injection but some are given orally (by mouth) or sprayed into the nose. *
Active immunization (= vaccination)

• It is is achieved by injecting a modified or purified pathogen or their products.

• Active immunization induced the immune system of an organism.

• It is achieved by injecting a recipient with performed antibodies or immunoglobulins. Passive immunization is used to provide immediate protection to individuals.

• Passive immunization does not induce the immune system of an organism.

1. Principle of vaccination is based on the property of 'memory' of the immune system. ]
2. During vaccination, antigenic proteins of pathogens or weakened pathogen (vaccine) is introduced into the body.
3. Antigens produce the primary immune response and the memory B and T-cells.
4. When the vaccinated person is attacked by the same pathogen, the existing memory T or B-cells recognize that antigen quickly and overwhelm and invaders with a massive production of Lymphocytes and antibodies.

Significance of vaccine 

• Vaccines reduce risks of getting a disease by working with your body's natural defenses to build protection.
• When we get vaccinated, we aren't just protecting overselves, but also those around us.
• When a person gets vaccinated against a disease their risk of infection is also reduced.
• Herd immunity is also known as 'population immunity is the indirect protection from an infections disease.
  
• In communities with high immunity, the non-immune people have lower risk of disease. 
  
• WHO supports achieving 'herd immunity' through vaccination, not by allowing a disease to spread. through a population.
  
• WHO estimates that vaccines save between 2 and 3 million lives every year.
  
• When you get a vaccine, your immune system responds.
  
• Vaccines used in national immunization programmes are extremely safe and effective.
• The purpose of a vaccine is to induce immunity by causing the receipient's immune system to react to the vaccine.