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

To achieve herd immunity — which protects members of the community who cannot get vaccines due to certain health conditions, vaccination rates should surpass 95%, according to the World Health Organization. —Post-Tribune, Chicago Tribune, 10 Apr. 2025

In Gaines County, the epicenter of the West Texas outbreak, only around 82% of kindergarteners were vaccinated for measles in the 2023-24 school year, compared to the 95% recommended by the World Health Organization to maintain herd immunity. —Olivia Aldridge, NPR, 8 Apr. 2025

But San Diego County, which has the second-largest number of kindergarten students after L.A. County, saw its immunization rate slip just below the 95% herd immunity benchmark to 94.8%. —Hannah Wiley, Los Angeles Times, 19 Mar. 2025

Officials also said the metro falls short of having herd immunity from the disease. —Pj Green, Kansas City Star, 19 Apr. 2025

Word History

First Known Use

1917, in the meaning defined above

Rhymes for herd immunity

• autoimmunity
• importunity
• opportunity
• community
• disunity
• impunity
• munity
• unity

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