Vaccine

A vaccine is a medical preparation given to provide immunity from a disease. Vaccines use a variety of different substances, ranging from dead microorganisms to genetically engineered antigens, to defend the body against potentially harmful microorganisms. Effective vaccines change the immune system by promoting the development of antibodies that can quickly and effectively attack a disease-causing microorganism when it enters the body, preventing disease development.

The development of vaccines against diseases ranging from polio and smallpox to tetanus and measles is considered one of the great accomplishments of medical science. Contemporary researchers are currently attempting to develop new vaccinations against such diseases as COVID–19, HIV/AIDS, malaria, influenza, and other diseases.

Physicians have long observed that individuals who were exposed to...