herd immunity


: 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
Serious 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

Examples of herd immunity in a Sentence

Recent Examples on the Web Research also shows that vaccines help build herd immunity and protect the body against disease. Solcyré Burga, TIME, 16 July 2024 That’s because the country has a good amount of herd immunity, either from vaccination, previous infections, or both. Michelle Marchante, Miami Herald, 11 July 2024 That herd immunity can protect people who can’t get vaccinated, such as those with weakened immune systems or serious allergies, by reducing their chances of infection. Tribune News Service, The Mercury News, 27 May 2024 According to this plan, the entire population would be vaccinated while case levels were low or nonexistent, thus allowing the country to achieve herd immunity without the devastating public health consequences that broader exposure to the virus might entail. Yanzhong Huang, Foreign Affairs, 26 Jan. 2022 See all Example Sentences for herd immunity 

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'herd immunity.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

Word History

First Known Use

1917, in the meaning defined above

Time Traveler
The first known use of herd immunity was in 1917

Dictionary Entries Near herd immunity

Cite this Entry

“Herd immunity.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/herd%20immunity. Accessed 25 Jul. 2024.

Kids Definition

herd immunity

: a reduction in the risk of catching a disease (as measles) that occurs when enough people have become immune to infection (as through previous exposure or vaccination) that susceptible people are far less likely to come in contact with infected people

Medical Definition

herd immunity

: 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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