Immunization refers to the process by which a person is made immune or resistant to an individual or set of infectious diseases, typically by giving the person a vaccine. Vaccines stimulate the body's immune system to protect the person from subsequent infections from the disease.

National vaccination programs around the world saved over 10 million lives between 2010 and 2015 and many millions of people were protected from falling ill.

Aside from preventing disease, vaccines also enable young children and adults in pursuing education and economic goals by ensuring that they are healthy enough to engage in these activities.

Despite immense progress in immunization coverage, over 19 million children under 1 year of age still did not get fully vaccinated in 2018.

Even though the emphasis of public health programs is usually on childhood vaccinations, adults also need certain vaccinations such as the influenza, hepatitis A, hepatitis B, and human papilloma virus vaccines, amongst others.

The safety of vaccines has been the subject of misinformation. Scientific evidence indicates that vaccines are very safe and side effects are usually mild and temporary. Serious side effects to vaccines are extremely rare, and in general, the quality of vaccines is assured by rigorous tests and quality checks.