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

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

The declaration called for speeding herd immunity by allowing people at low risk to get infected while protecting those most vulnerable, like the elderly. —Rob Stein, NPR, 26 Nov. 2024

China would need to vaccinate 70 to 80 percent of its population in order to meet the requirements of herd immunity. —Yanzhong Huang, Foreign Affairs, 11 Mar. 2021

In 2020, then NIH director Francis Collins and other public health officials rejected the Great Barrington Declaration, an open letter which Bhattacharya co-authored that argued against lockdowns and promoted herd immunity during the coronavirus pandemic. —Yaakov Katz, Newsweek, 28 Nov. 2024

His nominee for secretary of Defense, Pete Hegseth, pushed for herd immunity in May 2020 and encouraged anti-lockdown protests. —Benjamin Mazer, The Atlantic, 25 Nov. 2024

Word History

First Known Use

1917, in the meaning defined above

Kids Definition

herd immunity

noun

: 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

noun

ˈhərd- 

: 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