According to the World Health Organization (WHO), immunization is the process by which individuals are made resistant to an infectious disease by being administered an antigenic material, such as a vaccine. Vaccines stimulate the body's own immune system to protect the person against subsequent infection or disease. Immunization can protect people from disease, disability, and death. Immunization is one of the most cost-effective public health interventions to date, saving millions of lives every year. Vaccination not only protects individuals but also helps prevent and control the spread of infectious diseases in both the vaccinated individual and in the community. Vaccines are safe, effective, and have few side effects. Vaccines are used to prevent a wide variety of diseases, including diphtheria, pertussis, tetanus, polio, measles, mumps, rubella, Haemophilus influenzae type b, hepatitis B, and rotavirus.