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herd immunity
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Three line graphs display the dramatic decline in reported cases of diphtheria, polio, and measles in the United States from 1920 to 2019, each showing a sharp drop after the introduction of their respective vaccines. Diphtheria cases fell after 1921, polio after 1955, and measles after 1963, illustrating the impact of mass vaccination programs. An inset highlights an increase in measles cases after 2010. Vaccines by the numbers A nurse administers a vaccine to a young girl in a crowded clinic, while other women and children wait in line behind her in Nagaon, Assam, India. Vaccine timeline
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herd immunity: References & Edit History

Additional Reading

Information on vaccination and herd immunity is presented in Stanley A. Plotkin, Walter A. Orenstein, and Paul A. Offit (eds.), Vaccines, 6th ed. (2013).

Article Contributors

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  • The Editors of Encyclopaedia Britannica
    Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree. They write new content and verify and edit content received from contributors.

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  • Brian K. Lee
    Brian K. Lee is an assistant professor at the School of Public Health, Drexel University.

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Article History

Type Description Contributor Date
Modified link of Web site: National Center for Biotechnology Information - PubMed Central - Strength and weakness of disease-induced herd immunity in networks. Aug 14, 2026
Add new Web site: Johns Hopkins University - Bloomberg School of Public Health - What Is Herd Immunity and How Can We Achieve It With Covid-19. Jul 03, 2026
Add new Web site: Yale Medicine - Herd Immunity: Will We Ever Get There? Mar 13, 2026
Add new Web site: Loyola Marymount University Pressbooks - Concepts in Biology - Herd Immunity. Jan 17, 2026
Cross-references added. Oct 24, 2025
Add new Web site: Academia - The Role of Herd Immunity in Control of Contagious Diseases (PDF). Jul 09, 2025
Add new Web site: Cell Press - Current Biology - Herd immunity. Apr 16, 2025
Images added. Feb 26, 2025
Article restructured and examples of herd immunity added. Feb 13, 2025
Add new Web site: The Lancet - A history of herd immunity. Jan 18, 2025
Add new Web site: Humanities and Social Sciences Communications - The effect of herd immunity thresholds on willingness to vaccinate. Jun 01, 2024
Add new Web site: PNAS - Herd immunity is an important—and often misunderstood—public health phenomenon. Dec 28, 2023
Add new Web site: WebMD - What to Know About Herd Immunity. Oct 20, 2023
Add new Web site: Verywell Health - What is Herd Immunity? Aug 11, 2023
Add new Web site: Mayo Clinic - Herd immunity and COVID-19: What you need to know. May 20, 2023
Add new Web site: Healthline - What is Herd Immunity and Could it Help Prevent COVID-19? Apr 06, 2023
Add new Web site: National Center for Biotechnology Information - PubMed Central - Strength and weakness of disease-induced herd immunity in networks. Feb 21, 2023
Add new Web site: Cleveland Clinic - Herd Immunity. Jan 13, 2023
Add new Web site: Public Broadcasting Service - NOVA - What is Herd Immunity? Mar 03, 2016
New bibliography added. Dec 20, 2013
New article added. Dec 20, 2013
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