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What is a vaccine?

Melissa K. Jones, Meghan A. Berryman, Kelley Lobean McKinley, and Jennifer C. Drew

Why are vaccines used?

The purpose of a vaccine is to expose an individual to a weakened pathogen, or part of a pathogen, to train the immune system to protect that individual from serious illnesses caused by infection from that virus or bacteria. Inoculation has been used for centuries in prevention of infectious diseases such as smallpox. A vaccine works by teaching the immune system to recognize and produce a response against the harmful microorganism so that disease is significantly reduced or does not develop at all. The major advantage is that the immune system receives training without the individual becoming sick or exposed to the active pathogen.

Most vaccines are given before an individual has been exposed to the harmful organism so protective immunity can develop. These vaccines are called prophylactic or preventative vaccines; the vast majority of vaccines fall into this category. There are also therapeutic vaccines, which are given to patients at the time of illness to enhance the immune system’s response.

When discussing vaccines, there are a few important terms to know.

  • Antigen: The part of the microorganism (specifically recognized by the body) that triggers the development of a protective immune response.
  • Antibody: The defense protein (made by the body) that recognizes the antigen and triggers killing of the harmful microbe.
  • Adjuvants: Substances that activate the immune system and are added to vaccines to enhance the immune response to the antigen.

Sometimes, protective immunity lasts for a person’s entire life, but in other cases, immunity diminishes over time. In the latter case, a vaccine booster is given. This booster dose exposes the immune system to the antigen an additional time to increase immunity to protective levels again.

Vaccines are given before a person has been exposed to the harmful microorganism. This is part of the reason that vaccinations are given to children. Vaccines are also given at different stages of childhood development (often referred to as a vaccination schedule) to produce optimal protective immunity. This is why some vaccines are given to babies, while others are given to children and teens and some are given only to adults. Vaccines are one of the most effective tools in preventative health care. They protect millions of people from preventable diseases each year and are estimated to save $70 billion in societal costs in the US alone. For these reasons, some vaccines (such as those against measles) are required for children to attend school. Others are highly recommended, but not required, such as the annual flu vaccine. Table 1 describes the six types of vaccines currently available.

Table 1. Common types and features of vaccines.

References

National Institute of Allergy and Infectious Diseases. 2019. “Vaccine Types.” Accessed January 7, 2021. https://www.niaid.nih.gov/research/vaccine-types

Office of Disease Prevention and Health Promotion. 2020. “Immunization and Infectious Diseases.” Accessed January 7, 2021. https://www.healthypeople.gov/2020/topics-objectives/topic/immunization-and-infectious-diseases

Peer Reviewed

Publication #MB008

Date: 6/9/2022

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About this Publication

This document is MB008, one of a series of the Department of Microbiology and Cell Science, UF/IFAS Extension. Original publication date May 2022. Visit the EDIS website at https://edis.ifas.ufl.edu for the currently supported version of this publication.

About the Authors

Melissa K. Jones, assistant professor, Department of Microbiology and Cell Science; Meghan A. Berryman, graduate research assistant, Department of Microbiology and Cell Science; Kelley Lobean McKinley, graduate research assistant, Department of Microbiology and Cell Science; and Jennifer C. Drew, senior lecturer and Extension coordinator, Department of Microbiology and Cell Science; UF/IFAS Extension, Gainesville, FL 32611.

Contacts

  • Jennifer Drew