pro·​phy·​lax·​is | \ ˌprō-fə-ˈlak-səs How to pronounce prophylaxis (audio) also ˌprä- \
plural prophylaxes\ ˌprō-​fə-​ˈlak-​ˌsēz How to pronounce prophylaxis (audio) also  ˌprä-​ \

Definition of prophylaxis

: measures designed to preserve health (as of an individual or of society) and prevent the spread of disease

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Did You Know?

In Greek, phylax means "guard", so prophylactic measures guard against disease by taking action ahead of time. Thus, for example, before the polio vaccine became available, prophylaxis against polio included avoiding crowds and public swimming pools. These days a well-known kind of prophylactic is used to prevent sexually transmitted diseases; but prophylactic measures only work when people use them.

Examples of prophylaxis in a Sentence

Recent Examples on the Web Prescriptions of PrEP, a preexposure prophylaxis that can prevent HIV infection, have also fallen sharply, according to new research presented at a conference last month. al, "Black people account for 27% of Alabama’s population and 70% of new HIV cases," 22 Apr. 2021 Treatment for humans who may have been exposed to rabies is highly effective and involves a series of injections given over three to four weeks, called post-exposure prophylaxis. Annie Berman, Anchorage Daily News, "Y-K Delta officials recommend residents vaccinate pets ‘as soon as possible’ after rabid foxes found," 21 Apr. 2021 The pandemic has also impacted the distribution of preexposure prophylaxis, or PrEP, a once-daily pill used to prevent HIV. Dr. Tarun Jain, ABC News, "HIV testing, treatment decreases during COVID-19 pandemic," 11 Mar. 2021 Antibody therapy was also a mainstay of infectious disease treatment before World War II, and still has some niche uses especially in post-exposure prophylaxis for several viral diseases. Arturo Casadevall, STAT, "For early testing of convalescent plasma, we were ‘building the plane while we were flying it’," 4 Mar. 2021 Luckily, the disease is also almost completely preventable—as long as the wound is thoroughly cleaned and a preemptive treatment, known as post-exposure prophylaxis, or PEP, is administered as quickly as possible before symptoms set in. Gustav Cappaert/undark, Popular Science, "Americans spend millions of dollars on rabies treatments each year. They don’t have to.," 25 Feb. 2021 There are other strategies that can also reduce HIV transmission risk, like condom use and taking pre-exposure prophylaxis (PrEP) or post-exposure prophylaxis (PEP), two medications that lower your risk of contracting the virus. Mathew Rodriguez, SELF, "Jonathan Van Ness on Vulnerability Hangovers, Dating With Intention, and Living With HIV in a Pandemic," 1 Dec. 2020 The White House staff knew Boulware had been working on post-exposure prophylaxis, and the president's doctor wanted to see the trial results. Adam Rogers, Wired, "The Strange and Twisted Tale of Hydroxychloroquine," 11 Nov. 2020 Cheaper and quicker tests are already becoming available, and fairly soon there may be antibody and other treatments which, given early, reduce the risk of severe disease, and which might even offer some degree of prophylaxis. The Economist, "The second wave of covid-19 has sent much of Europe back into lockdown," 7 Nov. 2020

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'prophylaxis.' 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 prophylaxis

1683, in the meaning defined above

History and Etymology for prophylaxis

New Latin, from Greek prophylaktikos

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Time Traveler for prophylaxis

Time Traveler

The first known use of prophylaxis was in 1683

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Statistics for prophylaxis

Last Updated

2 May 2021

Cite this Entry

“Prophylaxis.” Dictionary, Merriam-Webster, Accessed 18 May. 2021.

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More Definitions for prophylaxis


pro·​phy·​lax·​is | \ -ˈlak-səs How to pronounce prophylaxis (audio) \
plural prophylaxes\ -​ˈlak-​ˌsēz How to pronounce prophylaxis (audio) \

Medical Definition of prophylaxis

: measures designed to preserve health and prevent the spread of disease : protective or preventive treatment prophylaxis against viral diseases a paste containing fluorine for dental prophylaxis

More from Merriam-Webster on prophylaxis

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

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