ana·​phy·​lax·​is | \ ˌa-nə-fə-ˈlak-səs How to pronounce anaphylaxis (audio) \
plural anaphylaxes\ ˌa-​nə-​fə-​ˈlak-​ˌsēz How to pronounce anaphylaxis (audio) \

Definition of anaphylaxis

1 : hypersensitivity (as to foreign proteins or drugs) resulting from sensitization following prior contact with the causative agent

Examples of anaphylaxis in a Sentence

Recent Examples on the Web Yet cases of anaphylaxis seem to only occur in about 5 in every million people vaccinated (and those who did have allergic reactions, meanwhile, responded positively to the use of an antihistamine, Bloomberg notes). Jeva Lange, The Week, 19 Aug. 2021 For instance, there were roughly 11 cases of anaphylaxis, a severe allergic reaction, for every million doses of the Pfizer vaccine administered, according to one C.D.C. study. New York Times, 8 Nov. 2021 The myocarditis cases are also more common than cases of anaphylaxis after the Hepatitis B vaccine (one in 1.1 million), which is required for elementary schoolers in all but a handful of states. Rachel Gutman, The Atlantic, 5 Nov. 2021 But anaphylaxis can be rough for those who do suffer from it. Ike Morgan |, al, 24 Dec. 2020 Last week, two nurses in the United Kingdom with a history of severe allergies developed anaphylaxis after being vaccinated. Matthew Herper, STAT, 18 Dec. 2020 The vaccine has also caused very rare anaphylaxis reactions. Washington Post, 19 Apr. 2021 Swelling or itching of the mouth or throat, hives, shortness of breath, GI problems, and in severe cases anaphylaxis, are all possible symptoms of a wheat allergy. Cynthia Sass, Mph,, 2 June 2021 In some cases, food allergies can lead to anaphylaxis, which is a life-threatening response that causes swelling in the airways, difficulty breathing, and potentially death if not treated quickly. Sarah Jacoby, SELF, 2 June 2021

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'anaphylaxis.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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First Known Use of anaphylaxis

circa 1905, in the meaning defined at sense 1

History and Etymology for anaphylaxis

New Latin, from ana- + prophylaxis

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Time Traveler for anaphylaxis

Time Traveler

The first known use of anaphylaxis was circa 1905

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Last Updated

4 Jan 2022

Cite this Entry

“Anaphylaxis.” Dictionary, Merriam-Webster, Accessed 24 Jan. 2022.

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More Definitions for anaphylaxis


ana·​phy·​lax·​is | \ ˌan-ə-fə-ˈlak-səs How to pronounce anaphylaxis (audio) \
plural anaphylaxes\ -​ˌsēz How to pronounce anaphylaxis (audio) \

Medical Definition of anaphylaxis

1 : hypersensitivity (as to foreign proteins or drugs) resulting from sensitization following prior contact with the causative agent

More from Merriam-Webster on anaphylaxis

Britannica English: Translation of anaphylaxis for Arabic Speakers Encyclopedia article about anaphylaxis


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