Although it was once thought to be uncommon in humans, cases increased since the 1980s, possibly as a result of waning immunity since the stopping of routine smallpox vaccination.Between 1981 and 1986  WHO surveillance in DRC/Zaire recorded 338 confirmed cases and 33 deaths (CFR 9.8%). In 1996–1997, a second outbreak of human illness was identified in DRC/Zaire and between 1991 and 1999, 511 cases were reported in DRC/Zaire. Clade I of disease remains endemic in DRC and has a higher CFR than the other genetic clade in Western Africa.By May 2022, the case fatality rate (CFR) of past outbreaks was around 3%–6%, while the CFR of the 2022 outbreak remains below 1%. No human-to-human transmission was documented until the 2022 monkeypox outbreak in Europe. Clade II had an outbreak – the first outbreak of monkeypox outside of Africa – in Midwestern United States among owners of pet prairie dogs in 2003. Seventy-one people were reportedly infected, of whom none died.As of 2018, monkeypox was traditionally restricted to the ecology of tropical rainforests. although the pattern was broken in 2005, when 49 cases were reported in Sudan (areas now South Sudan), with no fatalities. The genetic analysis suggested that the virus did not originate in Sudan but was imported, most likely from DRC.Many more monkeypox cases have been reported in Central and West Africa, and in the Democratic Republic of Congo in particular: 2000 cases per year are known between 2011 and 2014.
This has not been conclusively demonstrated in humans because routine smallpox vaccination was discontinued following the eradication of smallpox.Smallpox vaccine has been reported to reduce the risk of monkeypox among previously vaccinated persons in Africa. The decrease in immunity to poxviruses in exposed populations is a factor in the prevalence of monkeypox. It is attributed to waning cross-protective immunity among those vaccinated before 1980, when mass smallpox vaccinations were discontinued, and to the gradually increasing proportion of unvaccinated individuals.The United States Centers for Disease Control and Prevention (CDC) recommends that persons investigating monkeypox outbreaks and involved in caring for infected individuals or animals should receive a smallpox vaccination to protect against monkeypox. Persons who have had close or intimate contact with individuals or animals confirmed to have monkeypox should also be vaccinated. However, the CDC does not recommend pre-exposure vaccination for unexposed veterinarians, veterinary staff, or animal control officers, unless such persons are involved in field investigations. No smallpox or monkeypox vaccine has been approved for use during pregnancy. The CDC recommends that healthcare providers don a full set of personal protective equipment (PPE) before caring for an infected person. This includes a gown, mask, goggles, and a disposable filtering respirator (such as an N95). An infected person should be isolated in preferably a negative air pressure room or at least a private exam room to keep others from possible contact.Monkeypox prevention cannot be simplified to just providing a vaccine.