Editing Yellow fever (section)

==Prevention==
Personal prevention of yellow fever includes vaccination and avoidance of mosquito bites in areas where yellow fever is endemic.<ref name="Yellow fever"/> Institutional measures for the prevention of yellow fever include vaccination programmes and measures to control mosquitoes. Programmes for distribution of mosquito nets for use in homes produce reductions in malaria and yellow fever. EPA-registered insect repellent is recommended when outdoors. Exposure for even a short time is enough for a potential mosquito bite. Long-sleeved clothing, long pants, and socks are useful for prevention. Applying larvicides to water-storage containers can help eliminate potential mosquito breeding sites. EPA-registered insecticide spray decreases the transmission of yellow fever.<ref>{{Cite web |url=https://www.cdc.gov/yellowfever/prevention/ |title=Prevention {{!}} Yellow Fever {{!}} CDC |website=www.cdc.gov |access-date=2016-10-26 |url-status=live |archive-url=https://web.archive.org/web/20161026165250/http://www.cdc.gov/yellowfever/prevention/ |archive-date=2016-10-26}}</ref>
* Use insect repellent when outdoors such as those containing [[DEET]], [[picaridin]], [[ethyl butylacetylaminopropionate]] (IR3535), or [[oil of lemon eucalyptus]] on exposed skin.<ref>{{Cite journal | vauthors = Lo WL, Mok KL, Yu Pui Ming SD |date=September 2018 |title=Which insect repellents should we choose? Implications from results of local market survey and review of current guidelines |journal=Hong Kong Journal of Emergency Medicine |volume=25 |issue=5 |pages=272–280 |doi=10.1177/1024907918773630 |doi-access=free }}</ref>
* Mosquitoes may bite through thin clothing, so spraying clothes with repellent containing [[permethrin]] or another EPA-registered repellent gives extra protection.<ref>{{Cite book | vauthors = Shmaefsky BR |url= https://books.google.com/books?id=9k2Z3UlFeZQC&pg=PA62 |title=Yellow Fever |date= November 2009 |publisher=Infobase Publishing |isbn=978-1-60413-231-1 |language=en}}</ref> Clothing treated with permethrin is commercially available. Mosquito repellents containing permethrin are not approved for application directly to the skin.<ref>{{Cite web |last=US EPA |first=OCSPP |date=2013-07-15 |title=Repellent-Treated Clothing |url=https://www.epa.gov/insect-repellents/repellent-treated-clothing |access-date=2022-04-25 |website=www.epa.gov |language=en}}</ref>
* The peak biting times for many mosquito species are dusk to dawn. However, ''A. aegypti'', one of the mosquitoes that transmit yellow fever virus, feeds during the daytime.<ref name="Frequently Asked Questions">{{Cite web |date=2020-02-26 |title=Frequently Asked Questions |url=https://www.cdc.gov/yellowfever/qa/index.html |access-date=2022-04-25 |website=www.cdc.gov |language=en-us}}</ref> Staying in accommodations with screened or air-conditioned rooms, particularly during peak biting times, also reduces the risk of mosquito bites.<ref name="Frequently Asked Questions"/>

===Vaccination===
{{Main|Yellow fever vaccine}}
[[File:Yellow fever certificate.JPG|thumb|The [[Carte Jaune|cover of a certificate]] that confirms the holder has been vaccinated against yellow fever|upright]]
[[File:Yellow fever vaccination travel requirements map.svg|thumb|400px|[[Yellow fever vaccine|Vaccination against yellow fever]] 10 days before entering this country/territory is required for travellers coming from...<ref name="WHO country list">{{Cite web |url=https://www.who.int/publications/m/item/countries-with-risk-of-yellow-fever-transmission-and-countries-requiring-yellow-fever-vaccination-(may-2021) |title=Countries with risk of yellow fever transmission and countries requiring yellow fever vaccination (May 2021) |work=World Health Organization |publisher=United Nations |date=26 May 2021 |access-date=16 January 2022}}</ref>
{{Legend|#008000|All countries}}
{{Legend|#00FF00|Risk countries (including airport transfers){{refn|group=note|name=transit explanation|Also required for travellers having transited (more than 12 hours) through a risk country's airport.}}}}
{{Legend|#FFFF00|Risk countries (excluding airport transfers){{refn|group=note|name=no transit|Not required for travellers having transited through a risk country's airport.}}}}
{{Legend|#D35F5F|No requirement (risk country){{refn|group=note|name=ArBrPe|The WHO has designated (parts of) Argentina, Brazil, and Peru as risk countries, but these countries do not require incoming travellers to vaccinate against yellow fever.}}}}
{{Legend|#C0C0C0|No requirement (non-risk country)}}]]

[[Vaccination]] is recommended for those traveling to affected areas, because non-native people tend to develop more severe illness when infected. Protection begins by the 10th day after vaccine administration in 95% of people,<ref name="pmid19520559">{{cite journal | vauthors = Barrett AD, Teuwen DE | title = Yellow fever vaccine - how does it work and why do rare cases of serious adverse events take place? | journal = Current Opinion in Immunology | volume = 21 | issue = 3 | pages = 308–313 | date = June 2009 | pmid = 19520559 | doi = 10.1016/j.coi.2009.05.018 }}</ref> and had been reported to last for at least 10 years. The [[World Health Organization]] (WHO) now states that a single dose of vaccine is sufficient to confer lifelong immunity against yellow fever disease.<ref>[https://www.who.int/mediacentre/news/releases/2013/yellow_fever_20130517/en/ WHO | Yellow fever vaccination booster not needed] {{webarchive|url=https://web.archive.org/web/20130609154615/http://www.who.int/mediacentre/news/releases/2013/yellow_fever_20130517/en/ |date=2013-06-09 }}. Who.int (2013-05-17). Retrieved on 2014-05-12.</ref> The attenuated live vaccine stem 17D was developed in 1937 by [[Max Theiler]].<ref name="pmid19520559"/> The WHO recommends routine vaccination for people living in affected areas between the 9th and 12th month after birth.<ref name=Toll2009/>

Up to one in four people experience fever, aches, local soreness, and redness at the injection site.<ref>[https://www.cdc.gov/vaccines/hcp/vis/vis-statements/yf.html Yellow Fever Vaccine Information Statement.] {{webarchive|url=https://web.archive.org/web/20130921061606/http://www.cdc.gov/vaccines/hcp/vis/vis-statements/yf.html |date=2013-09-21 }} Centers for Disease Control and Prevention. March 30, 2011.</ref> In rare cases (less than one in 200,000 to 300,000),<ref name="pmid19520559"/> the vaccination can cause yellow fever vaccine-associated viscerotropic disease, which is fatal in 60% of cases. It is probably due to the genetic morphology of the immune system. Another possible side effect is an infection of the nervous system, which occurs in one in 200,000 to 300,000 cases, causing yellow fever vaccine-associated neurotropic disease, which can lead to [[meningoencephalitis]] and is fatal in less than 5%<ref name="pmid19520559"/> of cases.<ref name=Toll2009/><ref name="pmid18061688"/>

The Yellow Fever Initiative, launched by the WHO in 2006, vaccinated more than 105&nbsp;million people in 14 countries in West Africa.<ref>{{cite web |title=Yellow fever |url=https://www.who.int/mediacentre/factsheets/fs100/en/ |website=World Health Organization |access-date=2 April 2017 |url-status=live |archive-url=https://web.archive.org/web/20170418024142/http://www.who.int/mediacentre/factsheets/fs100/en/ |archive-date=18 April 2017}}</ref> No outbreaks were reported during 2015. The campaign was supported by the [[GAVI]] alliance and governmental organizations in Europe and Africa.<ref>{{Cite web |title=Measles vaccination has saved an estimated 17.1 million lives since 2000 |url=https://www.who.int/news/item/12-11-2015-measles-vaccination-has-saved-an-estimated-17-1-million-lives-since-2000 |access-date=2022-04-25 |website=World Health Organization |language=en}}</ref> According to the WHO, mass vaccination cannot eliminate yellow fever because of the vast number of infected mosquitoes in urban areas of the target countries, but it will significantly reduce the number of people infected.<ref name=BBC_vaccination>{{cite news |url=http://news.bbc.co.uk/1/hi/world/africa/8373960.stm |title=Twelve million West Africans get yellow fever vaccines |date=23 November 2009 |work=BBC News |access-date=23 November 2009 |url-status=live |archive-url=https://web.archive.org/web/20170908222719/http://news.bbc.co.uk/1/hi/world/africa/8373960.stm |archive-date=8 September 2017}}</ref>

Demand for yellow fever vaccines has continued to increase due to the growing number of countries implementing yellow fever vaccination as part of their routine immunization programmes.<ref name=WHO2016>{{cite web |title=Fractional Dose Yellow Fever Vaccine as a Dose-sparing Option for Outbreak Response. WHO Secretariat Information Paper. Department of Immunization, Vaccines and Biologicals. WHO reference number: WHO/YF/SAGE/16.1. |url=http://apps.who.int/iris/bitstream/handle/10665/246236/WHO-YF-SAGE-16.1-eng.pdf;jsessionid=F4BD11CEBB8426D52C781267F9795A8A?sequence=1 |date=20 July 2016 |publisher=World Health Organization |access-date=2 September 2018}}</ref> Recent upsurges in yellow fever outbreaks in Angola (2015), the Democratic Republic of Congo (2016), Uganda (2016), and more recently in Nigeria and Brazil in 2017 have further increased demand, while straining global vaccine supply.<ref name=WHO2016 /><ref>{{cite web |title=WHO supports the immunization of 874,000 people against yellow fever in Nigeria. News Release. |url=https://www.who.int/mediacentre/news/releases/2017/immunization-yellowfever-nigeria/en/ |date=16 October 2017 |publisher=World Health Organization |access-date=2 September 2018}}</ref> Therefore, to vaccinate susceptible populations in preventive mass immunization campaigns during outbreaks, [[Fractional dose vaccination|fractional dosing]] of the vaccine is being considered as a dose-sparing strategy to maximize limited vaccine supplies.<ref name=WHO2016 /> Fractional dose yellow fever vaccination refers to administration of a reduced volume of vaccine dose, which has been reconstituted as per manufacturer recommendations.<ref name=WHO2016 /><ref name="pmid28596091">{{cite journal | author = World Health Organization | title = Human papillomavirus vaccines: WHO position paper, May 2017-Recommendations | journal = Vaccine | volume = 35 | issue = 43 | pages = 5753–5755 | date = October 2017 | pmid = 28596091 | doi = 10.1016/j.vaccine.2017.05.069 }}</ref> The first practical use of fractional dose yellow fever vaccination was in response to a large yellow fever outbreak in the Democratic Republic of the Congo in mid-2016.<ref name=WHO2016 /> Available evidence shows that fractional dose yellow fever vaccination induces a level of immune response similar to that of the standard full dose.<ref name="pmid31859201">{{cite journal |vauthors=Nnaji CA, Shey MS, Adetokunboh OO, Wiysonge CS | title = Immunogenicity and safety of fractional dose yellow fever vaccination: A systematic review and meta-analysis | journal = Vaccine | volume = 38 | issue = 6 | pages = 1291–1301 | date = February 2020 | pmid = 31859201 | doi = 10.1016/j.vaccine.2019.12.018 }}</ref>

In March 2017, the WHO launched a vaccination campaign in Brazil with 3.5&nbsp;million doses from an emergency stockpile.<ref>{{cite web |title=WHO dispatched 3.5 million doses of yellow fever vaccine for outbreak response in Brazil |url=https://www.who.int/csr/disease/yellowfev/vaccination-in-Brazil/en/ |website=World Health Organization |access-date=2 April 2017 |url-status=live |archive-url=https://web.archive.org/web/20170401134133/http://www.who.int/csr/disease/yellowfev/vaccination-in-Brazil/en/ |archive-date=1 April 2017}}</ref> In March 2017 the WHO recommended vaccination for travellers to certain parts of Brazil.<ref name="Yellow fever – Brazil">{{cite journal |title=Yellow fever – Brazil |journal=Nature |volume=150 |issue=3811 |page=573 |bibcode=1942Natur.150T.573. |year=1942 |doi=10.1038/150573d0 |doi-access=free}}</ref> In March 2018, Brazil shifted its policy and announced it planned to vaccinate all 77.5&nbsp;million currently unvaccinated citizens by April 2019.<ref>{{cite news | vauthors = Darlington S |title=Fearing New Outbreaks, Brazil Will Vaccinate Country Against Yellow Fever |url=https://www.nytimes.com/2018/03/20/world/americas/yellow-fever-brazil-vaccinate.html |access-date=21 March 2018 |work=The New York Times |date=20 March 2018}}</ref>

====Compulsory vaccination====
Some countries in Asia are considered to be potentially in danger of yellow fever epidemics, as both mosquitoes with the capability to transmit yellow fever as well as susceptible monkeys are present.<ref>{{cite journal | vauthors = Kuno G | title = The Absence of Yellow Fever in Asia: History, Hypotheses, Vector Dispersal, Possibility of YF in Asia, and Other Enigmas | journal = Viruses | volume = 12 | issue = 12 | page = 1349 | date = November 2020 | pmid = 33255615 | pmc = 7759908 | doi = 10.3390/v12121349 | doi-access = free }}</ref> The disease does not yet occur in Asia. To prevent the introduction of the virus, some countries demand previous vaccination of foreign visitors who have passed through yellow fever areas.<ref>{{cite journal | vauthors = Wasserman S, Tambyah PA, Lim PL | title = Yellow fever cases in Asia: primed for an epidemic | journal = International Journal of Infectious Diseases | volume = 48 | pages = 98–103 | date = July 2016 | pmid = 27156836 | doi = 10.1016/j.ijid.2016.04.025 | doi-access = free | hdl = 10220/47081 | hdl-access = free }}</ref> Vaccination has to be proved by a vaccination certificate, which is valid 10 days after the vaccination and lasts for 10 years. Although the WHO on 17 May 2013 advised that subsequent booster vaccinations are unnecessary, an older (than 10 years) certificate may not be acceptable at all border posts in all affected countries. A list of the countries that require yellow fever vaccination is published by the WHO.<ref name="WHO country list"/> If the vaccination cannot be given for some reason, dispensation may be possible. In this case, an exemption certificate issued by a WHO-approved vaccination center is required. Although 32 of 44 countries where yellow fever occurs endemically do have vaccination programmes, in many of these countries, less than 50% of their population is vaccinated.<ref name=Toll2009/>

===Vector control===
[[File:Luchemos todos contra el dengue.jpg|thumb|left|Information campaign for prevention of [[dengue]] and yellow fever in [[Paraguay]]]]

Control of the yellow fever mosquito ''A. aegypti'' is of major importance, especially because the same mosquito can also transmit [[dengue]] fever and [[chikungunya]] disease.<ref>{{Cite web |title=Vector-borne diseases |url=https://www.who.int/news-room/fact-sheets/detail/vector-borne-diseases |access-date=2022-04-25 |website=World Health Organization |language=en}}</ref> ''A. aegypti'' breeds preferentially in water, for example, in installations by inhabitants of areas with precarious drinking water supplies, or in domestic refuse, especially tires, cans, and plastic bottles. These conditions are common in urban areas in developing countries.<ref>{{Cite web |title=Humanitarian emergencies |url=https://www.who.int/teams/environment-climate-change-and-health/water-sanitation-and-health/environmental-health-in-emergencies/humanitarian-emergencies |access-date=2022-04-25 |website=World Health Organization |language=en}}</ref>

Two main strategies are employed to reduce ''A. aegypti'' populations.<ref>{{cite journal | vauthors = Singh RK, Dhama K, Khandia R, Munjal A, Karthik K, Tiwari R, Chakraborty S, Malik YS, Bueno-Marí R | display-authors = 6 | title = Prevention and Control Strategies to Counter Zika Virus, a Special Focus on Intervention Approaches against Vector Mosquitoes-Current Updates | journal = Frontiers in Microbiology | volume = 9 | page = 87 | date = 2018 | pmid = 29472902 | doi = 10.3389/fmicb.2018.00087 | pmc = 5809424 | doi-access = free }}</ref> One approach is to kill the developing larvae. Measures are taken to reduce the water accumulations in which the larvae develop. [[Larvicide]]s are used, along with larvae-eating fish and [[copepod]]s, which reduce the number of larvae.<ref>{{Cite web |last=US EPA |first=OCSPP |date=2013-02-21 |title=Controlling Mosquitoes at the Larval Stage |url=https://www.epa.gov/mosquitocontrol/controlling-mosquitoes-larval-stage |access-date=2022-04-25 |website=www.epa.gov |language=en}}</ref> For many years, copepods of the genus ''[[Mesocyclops]]'' have been used in [[Vietnam]] for preventing dengue fever.<ref>{{cite journal | vauthors = Tran TT, Olsen A, Viennet E, Sleigh A | title = Social sustainability of Mesocyclops biological control for dengue in South Vietnam | journal = Acta Tropica | volume = 141 | issue = Pt A | pages = 54–59 | date = January 2015 | pmid = 25312335 | doi = 10.1016/j.actatropica.2014.10.006 | doi-access = free }}</ref> This eradicated the mosquito vector in several areas. Similar efforts may prove effective against yellow fever. [[Pyriproxyfen]] is recommended as a chemical larvicide, mainly because it is safe for humans and effective in small doses.<ref name=Toll2009/>

The second strategy is to reduce populations of the adult yellow fever mosquito. [[Lethal ovitrap]]s can reduce ''Aedes'' populations, using lesser amounts of pesticide because it targets the pest directly.<ref>{{cite journal | vauthors = Hustedt JC, Boyce R, Bradley J, Hii J, Alexander N | title = Use of pyriproxyfen in control of Aedes mosquitoes: A systematic review | journal = PLOS Neglected Tropical Diseases | volume = 14 | issue = 6 | pages = e0008205 | date = June 2020 | pmid = 32530915 | pmc = 7314096 | doi = 10.1371/journal.pntd.0008205 | doi-access = free }}</ref> Curtains and lids of water tanks can be sprayed with [[insecticide]]s, but application inside houses is not recommended by the WHO.<ref>{{cite journal | vauthors = Pérez D, Van der Stuyft P, Toledo ME, Ceballos E, Fabré F, Lefèvre P | title = Insecticide treated curtains and residual insecticide treatment to control Aedes aegypti: An acceptability study in Santiago de Cuba | journal = PLOS Neglected Tropical Diseases | volume = 12 | issue = 1 | pages = e0006115 | date = January 2018 | pmid = 29293501 | pmc = 5766245 | doi = 10.1371/journal.pntd.0006115 | doi-access = free }}</ref> Insecticide-treated [[mosquito net]]s are effective, just as they are against the ''[[Anopheles]]'' mosquito that carries malaria.<ref name=Toll2009/>