Male circumcision reduces the risk of human immunodeficiency virus (HIV) transmission from HIV positive women to men in high risk populations. In 2020, the World Health Organization (WHO) reiterated that male circumcision is an efficacious intervention for HIV prevention if carried out by medical professionals under safe conditions. Circumcision reduces the risk that a man will acquire HIV and other sexually transmitted infections (STIs) from an infected female partner through vaginal sex. The evidence regarding whether circumcision helps prevent HIV is not as clear among men who have sex with men (MSM). The effectiveness of using circumcision to prevent HIV in the developed world is not determined. Efficacy Heterosexual men , past research has shown that circumcision reduces the risk of HIV infection in heterosexual men, although these studies have had limitations. The WHO Expert Group on Models To Inform Fast Tracking Voluntary Medical Male Circumcision In HIV Combination Prevention in 2016 found "large benefits" of circumcision in settings with high HIV prevalence and low circumcision prevalence. The Group estimated male circumcision is cost-saving in almost all high priority countries. Furthermore, WHO stated that: "While circumcision reduces a man’s individual lifetime HIV risk, the indirect effect of preventing further HIV transmissions to women, their babies (vertical transmission) and from women to other men has an even greater impact on the population incidence, particularly for circumcisions performed at younger ages (under age 25 years)." Newly-circumcised HIV infected men who are not taking antiretroviral therapy can shed the HIV virus from the circumcision wound, thus increasing the immediate risk of HIV transmission to female partners. This risk of post-operative transmission presents a challenge, although in the long-term it is possible the circumcision of HIV-infected men helps lessen heterosexual HIV transmission overall. Such viral shedding can be mitigated by the use of antiretroviral drugs. Additional research is needed to ascertain the existence and potential risk of viral shedding from circumcision wounds. Men who have sex with men The WHO does not recommend circumcision as protection against male to male HIV transmission, as evidence is lacking in regards to receptive anal intercourse. The WHO also states that MSM should not be excluded from circumcision services in countries in eastern and southern Africa, and that circumcision may be effective at limiting the spread of HIV for MSM if they also engage in vaginal sex with women. Regional differences Whether circumcision is beneficial to developed countries