herd immunity

From herd + immunity, first identified in herds of cattle.^[1]

• (Received Pronunciation) IPA^(key): /ˈhəːd ɪˈmjuːnɪti/

• Audio (Southern England):

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• (General American) IPA^(key): /ˈhɚd ɪˈmjunəti/,
• Hyphenation: herd im‧mun‧ity

herd immunity (countable and uncountable, plural herd immunities)

1. (epidemiology) The indirect protection against the spread of a contagious disease in a given population caused by the immunity of a significant proportion of the population to that particular disease; the immunity may have been obtained through having survived the infection or through vaccination.
   • 1917 January, Adolph Eichhorn, George M. Potter, “Prevention and Treatment”, in Contagious Abortion of Cattle (United States Department of Agriculture Farmers’ Bulletin; 790), Washington, D.C.: Government Printing Office, →OCLC, page 9:

     During the years that the herd was being replenished by purchase abortions were frequent, but that practice was discontinued, and the heifer calves born in the herd have been raised. [...] Thus a herd immunity seems to have developed as a result both of keeping the aborting cows and raising the calves.

   • 1923 May, W[illiam] W[hiteman] C[arlton] Topley, G[raham] S[elby] Wilson, “The Spread of Bacterial Infection. The Problem of Herd-Immunity.”, in The Journal of Hygiene‎, volume 21, number 3, London: Cambridge University Press, →DOI, →ISSN, →OCLC, →PMID, archived from the original on 2 April 2020, page 243:

     The Spread of Bacterial Infection. The Problem of Herd-Immunity [title]. [...] Consideration of the results obtained over the last five years, [...] has led us to believe that the question of immunity as an attribute of a herd should be studied as a separate problem, closely related to, but in many ways distinct from, the problem of the immunity of an individual host.

   • 1956, L. O. Mott, C. A. Manthei, “Miscellaneous Diseases of Cattle”, in Alfred Stefferud, editor, Yearbook of Agriculture 1956: Animal Diseases (United States Congress, House Document; no. 344), Washington, D.C.: The United States Government Printing Office, →OCLC, page 329, column 1:

     It is likely that many animals in affected herds have developed an inapparent or nonclinical form of the disease because there have been no records of recurrence of the disease on the same farm—an indication that a herd immunity developed.

   • 1978, G. J. Ebrahim, Practical Mother and Child Health in Developing Countries (Macmillan Tropical Community Health Manuals), revised edition, London: The Macmillan Press, →ISBN; ELBS edition, London: English Language Book Society and Macmillan Education, 1980 (1982 printing), →ISBN, page 56:

     The larger the number of immunised people in the community the less easy is the spread of disease from one person to another. [...] For the purpose of creating ‘herd immunity’, as this process is sometimes called, it is necessary to achieve 80 per cent immunisation of the community.

   • 1994, Alan M. Kraut, “‘The Old Inquisition had Its Rack and Thumbscrews’: Immigrant Health and the American Workplace”, in Silent Travelers: Germs, Genes, and the “Immigrant Menace”, New York, N.Y.: Basic Books, →ISBN; Johns Hopkins Paperbacks edition, Baltimore, Md., London: Johns Hopkins University Press, 1995, →ISBN, page 147:

     Jews, long exposed to some diseases in the confined quarters of European ghettos, had developed herd immunities through a long process of natural selection.

   • 1995, Luis Enjuanes, Bernard A. M. Van der Zeijst, “Molecular Basis of Transmissible Gastroenteritis Virus Epidemiology”, in Stuart Siddell, editor, The Coronaviridae (The Viruses), New York, N.Y.: Plenum Press, →ISBN, page 337:

     The disease incidence appeared to have a cyclic course. After an outbreak, the disease and virus disappeared and the herd immunity gradually waned in the next 2 to 3 years. A new outbreak was the consequence of the reintroduction of transmissible gastroenteritis virus (TGEV).

   • 2006, Warren Levinson, Review of Medical Microbiology and Immunology, 9th edition, New York, N.Y.: Lange Medical Books/McGraw-Hill, →ISBN, page 247:

     For herd immunity to occur, the vaccine must prevent transmission of the virus as well as prevent disease.

   • 2007, D. Caroline Coile, “Maintaining Your Pom’s Health and Happiness”, in Pomeranians for Dummies (For Dummies), Hoboken, N.J.: John Wiley & Sons, →ISBN, part III (Caring for Your Pom from Head to Paw), page 152:

     Some proponents of natural rearing condemn vaccinations; they prefer using homeopathic nosodes (medicine prepared from the diseased part or discharge of something, which supposedly works as well as vaccination). These people point to their dogs' good health as proof that nosodes work. However, their good fortune is probably the result of herd immunity, that is, as long as most dogs are vaccinated, the unvaccinated dogs rarely come in contact with the infectious agents.

   • 2010, Ray M. Merrill, “Practical Disease Concepts in Epidemiology”, in Introduction to Epidemiology, 5th edition, Sudbury, Mass.: Jones and Bartlett Publishers, →ISBN, page 65:

     Herd immunity is based on the notion that if a herd (a population or a group) is mostly protected from a disease by immunization then the chance that a major epidemic will occur is limited. Jonas Salk, one of the developers of the polio vaccine, suggested that if a herd immunity level of 85% exists in a population, a polio epidemic will not occur. Herd immunity is also viewed as the resistance a population has to the invasion and spread of an infectious disease.

   • 2011 April 1, Paul Fine, Ken Eames, David L. Heymann, “‘Herd Immunity’: A Rough Guide”, in Clinical Infectious Diseases, volume 52, number 7, Oxford, Oxfordshire: Oxford University Press for the Infectious Diseases Society of America, →DOI, →ISSN, →OCLC, →PMID, page 911:

     Many examples of herd immunity have been described, illustrating the importance of indirect protection for predicting the short- and long-term impact of vaccination programs, for justifying them economically, and for understanding the nature of the immunity induced by various vaccines.

   • 2014, Paul Reiter, “Surveillance and Control of Urban Dengue Vectors”, in Duane J. Gubler, Eng Eong Ooi, Subhash Vasudevan, Jeremy Farrar, editors, Dengue and Dengue Hemorrhagic Fever, 2nd edition, Wallingford, Oxfordshire, Boston, Mass.: CABI, →ISBN, part V (Dengue Prevention), page 500, column 1:

     At above 80% immunity, the simulation indicates that no transmission can occur, even when mosquito densities are high (5 per person). Similar herd immunities (82–87%) halt transmisson of poliomyelitis and diphtheria. At lower herd immunities, transmission occurs at increasingly lower vector densities.

   • 2020 April 2, Zeynep Tufekci, “Don’t Believe the COVID-19 Models: That’s Not What They’re For”, in Jeffrey Goldberg, editor, The Atlantic‎, Washington, D.C.: The Atlantic Monthly Group, →ISSN, →OCLC, archived from the original on 2 April 2020:

     A few weeks ago, the U.K. had almost no social-isolation measures in place, and according to some reports, the government planned to let the virus run its course through the population, with the exception of the elderly, who were to be kept indoors. The idea was to let enough people get sick and recover from the mild version of the disease, to create "herd immunity." Things changed swiftly after an epidemiological model from Imperial College London projected that without drastic interventions, more than half a million Britons would die from COVID-19.

• herd immunity on Wikipedia.Wikipedia