herd immunity
noun
: a reduction in the risk of infection with a specific communicable disease (such as measles or influenza) that occurs when a significant proportion of the population has become immune to infection (as because of previous exposure or vaccination) so that susceptible individuals are much less likely to come in contact with infected individuals
… when the percentage of people vaccinated against a particular disease drops, herd immunity begins to fail.—
Katherine Hobson
Katherine HobsonSerious streptococcal disease does seem to be on the rise, however, perhaps because invasive strains are circulating against which we have not had time to develop much "herd immunity," as epidemiologists say.—Wayne Biddle
Wayne BiddleExamples of herd immunity in a Sentence
Recent Examples on the Web
Vaccine rates have declined by an average of 2.67% in most U.S. counties over the past five years, according to data published by John Hopkins University, resulting in a growing number of states moving further away from the 95% herd immunity threshold.
—Alyssa Goldberg, USA Today, 18 June 2025
Medical experts put the vaccination herd immunity rate for measles at around 95%.
—Joseph States, Chicago Tribune, 12 June 2025
But once herd immunity is achieved, individual parents may decide that not vaccinating is the less risky option for their kid.
—Avi Dor, The Conversation, 5 June 2025
Below that threshold, a community's herd immunity can begin to erode.
—Maria Godoy, NPR, 9 May 2025
See All Example Sentences for herd immunity
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Alyssa Goldberg, USA Today, 18 June 2025
Medical experts put the vaccination herd immunity rate for measles at around 95%.
—Joseph States, Chicago Tribune, 12 June 2025
But once herd immunity is achieved, individual parents may decide that not vaccinating is the less risky option for their kid.
—Avi Dor, The Conversation, 5 June 2025
Below that threshold, a community's herd immunity can begin to erode.
—Maria Godoy, NPR, 9 May 2025
See All Example Sentences for herd immunity
Cite this Entry
“Herd immunity.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/herd%20immunity. Accessed 5 Jul. 2025.
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herd immunity
noun
: a reduction in the probability of infection that is held to apply to susceptible members of a population in which a significant proportion of the individuals are immune because the chance of coming in contact with an infected individual is less
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