2022–2023 mpox outbreak

In May 2022, the World Health Organization (WHO) made an emergency announcement of the existence of a multi-country outbreak of mpox, a viral disease then commonly known as "monkeypox". The initial cluster of cases was found in the United Kingdom, where the first case was detected in London on 6 May 2022 in a patient with a recent travel history from Nigeria where the disease has been endemic. On 16 May, the UK Health Security Agency (UKHSA) confirmed four new cases with no link to travel to a country where mpox is endemic. Subsequently, cases have been reported from many countries and regions. The outbreak marked the first time mpox had spread widely outside Central and West Africa. The disease had been circulating and evolving in human hosts over several years before the outbreak and was caused by the clade IIb variant of the virus.

On 23 July 2022, the director-general of the WHO, Tedros Adhanom Ghebreyesus, declared the outbreak a public health emergency of international concern (PHEIC), stating that "we have an outbreak that has spread around the world rapidly, through new modes of transmission, about which we understand too little". A global response to the outbreak included public awareness campaigns in order to reduce spread of the disease, and repurposing of smallpox vaccines.

In May 2023, the World Health Organization declared an end to the PHEIC, citing steady progress in controlling the spread of the disease. Relatively low levels of cases continued to occur, and as of 31 December 2025, there have been a total of 173,692 confirmed cases and 476 deaths in 143 countries.

Mpox is a viral infection that manifests a week or two after exposure with fever and other non-specific symptoms, and then produces a rash with lesions that usually last for 2–4 weeks before drying up, crusting and falling off. While mpox can cause large numbers of lesions, in this outbreak some patients experience only a single lesion in the mouth or on the genitals, making it more difficult to differentiate from other infections. In previous outbreaks, 1–3 per cent of people with known infections had died (without treatment). In the 2022–2023 outbreak the rate of death was less than 0.2 percent. Cases in children and immunocompromised people are more likely to be severe.

Mpox spreads through close, personal, often skin-to-skin contact. The disease can spread through direct contact with rashes, or body fluids from an infected person, by touching objects and fabrics that have been used by someone with mpox or through respiratory secretions. Given the unexpected and vast geographical spread of the disease, the actual number of cases is likely to be underestimated. While anyone can get mpox, the majority of confirmed cases outside of the endemic regions in Africa occurred in young or middle-aged men who have sex with men (MSM) who had recent sexual contact with new or multiple partners. On 28 July 2022, the WHO Director-General advised MSM to limit exposure by reducing the number of sexual partners, reconsidering sex with new partners, and maintaining contact details to allow for epidemiological follow-up. The Centers for Disease Control and Prevention has emphasized the importance of reducing stigma in communicating about the demographic aspects of mpox, specifically with regards to gay and bisexual men.

A new outbreak of a different variant of mpox began in 2023 and was declared a PHEIC in August 2024.

Background

Emergency preparedness prior to outbreak

On 17 March 2021, the Nuclear Threat Initiative led a tabletop exercise at the Munich Security Conference simulating hypothetical public health responses to the intentional release of a genetically manipulated strain of monkeypox virus. On 23 July 2022, the World Health Organization Director-General Tedros Adhanom Ghebreyesus declared the 2022 outbreak a public health emergency of international concern. In May 2023, the emergency was declared over.

Endemic mpox in Africa

Mpox is endemic to West and Central Africa.

In a 2021 article, Oyewale Tomori pointed out that the number of mpox infections in Nigeria through 2021 were likely to be under-reported, because many Nigerians had been avoiding healthcare facilities due to fear of contracting COVID-19. Nigeria's surveillance of various diseases, including mpox, had to focus on the global COVID-19 pandemic in 2020 and 2021, missing many cases and resulting in a drop in official statistics.

As British health authorities reported the first case of mpox in the UK in May 2022, the Nigerian government released information and statistics on reported cases and deaths in the country: The report of 9 May 2022 stated that between 2017 and 2022 there were 230 confirmed cases across 20 states and the Federal Capital Territory. Rivers State was the most affected, followed by Bayelsa and Lagos. In the span from 2017 to 2022, the NCDC reported six deaths in six different states, making for a 3.3% case fatality ratio. On 30 May, the first death from mpox was reported in Nigeria during 2022; the last time a death was reported in the country from this disease was in 2019.

In May 2022 the Africa Centres for Disease Control and Prevention alerted several members of the African Union about cases of mpox. The director of the Africa CDC, Ahmed Ogwell, said that Cameroon, Central African Republic, the Democratic Republic of Congo and Nigeria have reported 1,405 endemic cases with 62 deaths during the first five months of 2022. The case fatality rate in these four African countries combined was 4.4%.

Outbreak characteristics

Prior to the 2022 outbreak, the United Kingdom had recorded only seven previous cases of mpox, all of which were imported cases from Africa or healthcare workers involved in their treatment. The first three such cases were in 2018, followed by a further case in 2019 and three more in 2021. The only major mpox outbreak to be recorded in a Western country prior to 2022 was the 2003 Midwest monkeypox outbreak in the United States, which did not feature community transmission.

Phylogenetics

Phylogenomic characterization of the first monkeypox virus outbreak genome sequences, found the "presumably slow-evolving" DNA virus has evolved roughly 6–12-fold more mutations than one would expect and 15 SNP mutations since the beginning of the outbreak. Examination of the mutations suggested they were the result of cytosine deamination by an APOBEC (apolipoprotein B mRNA editing enzyme, catalytic polypeptide) protein expressed in the human cells. Recombination has been reported in the natural transmission of monkeypox virus. Using Tandem repeat polymorphism, case FVGITA-01 (ON755039) in Italy, case VIDRL01(ON631963) in Australia, as well as six cases in Slovenia (ON838178, ON631241, ON609725, ON754985, ON754986, ON754987) were recombinant crossovers. Based on linkage disequilibrium (LD) between monkeypox virus variants with minor alleles in at least two MPXV isolates and to detect the possible recombination, two Germany cases (ON959149 and ON637939) and one Spain case (ON720849) already gained their mutations via recombination. Scientists investigated circulating lineages (and potential variants) of the monkeypox virus and are comparing them against the African endemic lineages.

Long incubation periods

Most mpox patients become symptomatic 4–11 days after infection. Very short incubation periods are also possible, with 5% of patients developing symptoms within 3 days. This outbreak revealed that incubation periods of up to 4 weeks are possible, with 5% of cases having incubation periods longer than the previously assumed 21 days.

Mild clinical manifestations

An analysis of studies by a journalist in August 2022 indicated that "about 10-to-15% of cases had been hospitalized, mostly for pain and bacterial infections that can occur as a result of mpox lesions". Studies published a month later, in August indicated hospitalizations of small cohorts of early patients were 8% and 13%. A short review suggested supportive care may typically be sufficient and that several antivirals and vaccinia immune globulin intravenous (VIGIV) are available as treatments. The outbreak showed there can be (rare) asymptomatic infections.

Fear of zoonotic spread

In May 2022, the UK Human Animal Infections and Risk Surveillance (HAIRS) group warned that the virus could reach wildlife and become endemic as a result. There was a concern that if the ongoing outbreak is prolonged, it "could establish new ecological niches in wild animals" in regions outside of Africa.

In August, the first known case of probable human-to-dog transmission was reported with the canine exhibiting very similar signs and symptoms of mpox infection to that of humans.