集団免疫

herd immunity

The strategy, an attempt to build “herd immunity,” involved allowing “enough of us who are going to get mild illness to become immune,” Sir Patrick Vallance, the U.K. government’s chief scientific adviser, told Sky News on March 13.
https://www.nationalgeographic.com/science/2020/03...

When Vallance was asked on Monday if the Japanese case meant herd immunity was no longer achievable, ...
https://www.theguardian.com/world/2020/mar/16/the-...

herdは herd of elephants などの表現でおなじみの「群れ」。この表現では形容詞的に用いられている。

報道記事から離れてこの用語をみるときは、下記2000年の論文のアブストが有益かも。
Eur J Epidemiol. 2000;16(7):601-6.
Herd immunity and herd effect: new insights and definitions.
John TJ1, Samuel R.
https://www.ncbi.nlm.nih.gov/pubmed/11078115

The term herd immunity has been used by various authors to conform to different definitions. Earlier this situation had been identified but not corrected. We propose that it should have precise meaning for which purpose a new definition is offered: "the proportion of subjects with immunity in a given population". This definition dissociates herd immunity from the indirect protection observed in the unimmunised segment of a population in which a large proportion is immunised, for which the term 'herd effect' is proposed. It is defined as: "the reduction of infection or disease in the unimmunised segment as a result of immunising a proportion of the population". Herd immunity can be measured by testing a sample of the population for the presence of the chosen immune parameter. Herd effect can be measured by quantifying the decline in incidence in the unimmunised segment of a population in which an immunisation programme is instituted. ...