Herd immunity

[[File:Community Immunity.jpg|thumb|right|165px|How it works]]{{sciencenav}}
'''Herd immunity''' is the idea that when a certain percentage of a population is vaccinated, those within the population who are not vaccinated are protected from the disease.  This is a fairly straightforward concept; if 90% of a population is immune, then the chances that a carrier of the disease will come into contact with a non-immune member of the population (or "herd") is low.<ref>[https://web.archive.org/web/20190211070931/http://www.mathepi.com/maindir/herd.html The mathematics of herd immunity] by Tom Lietman (2000) ''Mathepi.Com'' (archived from February 11, 2019).</ref>

The average number of people that an infected person can infect (R<sub>0</sub>) for a given disease is corresponds to the percentage of a population that needs to be vaccinated to achieve herd immunity (1-1/R<sub>0</sub>). Hence, highly-transmissible [[measles]] (R<sub>0</sub> = 12 to 18) needs a high percentage of the population to be vaccinated (92-95%). Conversely, [[Ebola]] has a relatively low R<sub>0</sub> (1.5 to 2.5) and the percentage of the population that would need to be vaccinated to achieve herd immunity is estimated to only be 42-63%.<ref>[https://www.sciencenews.org/article/one-number-can-help-explain-why-measles-so-contagious One number can help explain why measles is so contagious: A disease's R<sub>0</sub> is the average number of people a person can infect in an unvaccinated population] by Helen Thompson (1:00pm, May 28, 2019) ''Science News''.</ref> The original 2019 strain of [[COVID]] only had an R<sub>0</sub> of 2-3, but the 2021 delta variant of COVID has an R<sub>0</sub> of 5-9, which compares to chicken pox with an R<sub>0</sub> of 8.5.<ref>[https://www.sfchronicle.com/health/article/CDC-says-the-delta-variant-is-as-contagious-as-16356370.php CDC says the delta variant is as contagious as chickenpox. Here's what that means] by Jessica Flores (Aug. 1, 2021) ''The San Francisco Chronicle''.</ref>

Herd immunity is the goal of most vaccination programs as it is the point where a disease can start to be eliminated altogether from a population, as is the case for polio in the [[Western World]].<ref>[http://www.polioeradication.org/Polioandprevention/Historyofpolio.aspx www.polioeradication.org timeline of worldwide cases of polio] Polio remains a problem in countries where vaccination is not sufficiently widespread.</ref>

While herd immunity by vaccine is vastly superior, the term also covers immunity in a community where a sufficient number of people have caught and recovered from an infection.<ref>[https://well.blogs.nytimes.com/2016/10/28/does-the-flu-provide-better-immunity-than-a-flu-shot/]</ref>

==History==
For example, in 1962 [[Japan]] instituted mandatory vaccination against [[influenza]] in school children. This continued until 1987 when the program was changed to optional; it was abandoned in 1994. Approximately 85% of children were estimated to have been vaccinated.<ref>[http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=387431 Control of Influenza]</ref> Several studies examined the mortality rates due to influenza during this period of time and revealed that the death rates due to influenza in all population groups was drastically decreased, including older adult populations. Since there was no increased rate of vaccination in these populations, the decreased mortality was caused by herd immunity effects of vaccinating so many children.<ref>[http://www.newsrx.com/newsletters/Vaccine-Weekly/2001-04-11/200104113335VW.html Mandatory Vaccination of Japanese Schoolchildren Demonstrates "Herd Immunity"]</ref> Many researchers have written that this and other evidence argues strongly for mandatory vaccination programs worldwide as a means of controlling many diseases and preventing a [[pandemic]].<ref> [http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1360502 Herd Immunity]</ref>

The [[United States]] has mandatory vaccination according to an official Center for Disease Control schedule. Enforcement is left to the states. Most states have medical and religious exemptions. Some states make it very easy to opt out of vaccines, while other states strictly enforce compliance for school attendance.

==COVID==
{{main|COVID-19}}
It has been proposed by some politicians that herd immunity via mass infection would solve the COVID pandemic, mainly based on the belief that  it would keep the economy going full steam ahead and get themselves reelected (most notably [[Boris Johnson]],<ref>[https://www.theatlantic.com/health/archive/2020/03/coronavirus-pandemic-herd-immunity-uk-boris-johnson/608065/ The U.K.'s Coronavirus ‘Herd Immunity’ Debacle: The country is not aiming for 60 percent of the populace to get COVID-19, but you’d be forgiven for thinking so based on how badly the actual plan has been explained.] by Ed Yong (March 16, 2020) ''The Atlantic''.</ref> and [[Donald Trump]]'s White House,<ref>[https://www.washingtonpost.com/politics/trump-coronavirus-scott-atlas-herd-immunity/2020/08/30/925e68fe-e93b-11ea-970a-64c73a1c2392_story.html New Trump pandemic adviser pushes controversial ‘herd immunity’ strategy, worrying public health officials] by Yasmeen Abutaleb & Yasmeen Abutaleb (August 31, 2020 at 12:56 p.m. PDT) ''The Washington Post''.</ref><ref>[https://www.washingtonpost.com/health/covid-herd-immunity/2020/10/10/3910251c-0a60-11eb-859b-f9c27abe638d_story.html Proposal to hasten herd immunity to the coronavirus grabs White House attention but appalls top scientists]  by Joel Achenbach (Oct. 13, 2020 at 11:30 a.m. PDT) ''The Washington Post''.</ref> and [[Sweden]]<ref>[https://www.sciencemag.org/news/2020/10/it-s-been-so-so-surreal-critics-sweden-s-lax-pandemic-policies-face-fierce-backlash 'It's been so, so surreal.' Critics of Sweden’s lax pandemic policies face fierce backlash] by Gretchen Vogel (Oct. 6, 2020 , 4:35 PM) ''Science''.</ref>). As a strategy however, this is "[[Science|scientifically]] and [[Morality|ethically]] problematic," according to Adhanom Ghebreyesus, head of the World Health Organization, because of all of the "unnecessary infections, suffering and [[death]]" that the strategy would cause.<ref>[https://www.washingtonpost.com/world/2020/10/13/herd-immunity-coronavirus-unethical-who/ Trying to reach herd immunity is 'unethical' and unprecedented, WHO head says] by Antonia Noori Farzan and Antonia Noori Farzan & Miriam Berger (Oct. 13, 2020 at 8:46 a.m. PDT) ''The Washington Post''.</ref>

Herd immunity via COVID-19 vaccination has been proposed throughout the pandemic, but has been blockaded by a flourishing [[anti-vaccination movement]] spreading [[bullshit]], while the Delta variant is considered infectious enough that eradicating the disease through herd immunity is now practically impossible, meaning that the end result is likely to be COVID simply becoming endemic in the world population.

==In a nutshell==
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==See also==
*[[Anti-vaccination movement]]

==External links==
*[https://www.theguardian.com/society/ng-interactive/2015/feb/05/-sp-watch-how-measles-outbreak-spreads-when-kids-get-vaccinated Watch how the measles outbreak spreads when kids get vaccinated – and when they don't] ''The Guardian''

==References==
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