2022–2023 mpox outbreak
In May 2022, the World Health Organization 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 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, 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. 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 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
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 protein expressed in the human cells. Recombination has been reported in the natural transmission of monkeypox virus. Using Tandem repeat polymorphism, case FVGITA-01 in Italy, case VIDRL01 in Australia, as well as six cases in Slovenia were recombinant crossovers. Based on linkage disequilibrium between monkeypox virus variants with minor alleles in at least two MPXV isolates and to detect the possible recombination, two Germany cases and one Spain case already gained their mutations via recombination.Scientists investigated circulating lineages 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 are available as treatments. The outbreak showed there can be asymptomatic infections.Fear of zoonotic spread
In May 2022, the UK Human Animal Infections and Risk Surveillance 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.
Chronology
In the beginning of May 2022, a case of mpox in a British resident who had travelled to Lagos and Delta State in Nigeria, in areas where mpox is considered to be an endemic disease, was reported. The person developed a rash on 29 April while in Nigeria and flew back to the United Kingdom, arriving on 4 May, and presented to hospital later the same day. Mpox infection was immediately suspected, and the patient was hospitalised at a specialist clinical unit of the Guy's and St Thomas' NHS Foundation Trust and isolated, then tested positive for the virus on 6 May. Testing of patient swab samples by polymerase chain reaction revealed clade II of monkeypox virus, which is the less deadly of the two known monkeypox virus variants with a case fatality rate of around 1%. The genomic sequence of the virus associated with this outbreak was first published on 19 May by Portuguese researchers.Extensive contact tracing of people who had been in contact with the index case both on the international flight from Nigeria to the United Kingdom and within the country following their arrival was carried out, with potential contacts advised to remain aware of the symptoms of mpox and immediately isolate if any were to develop within 21 days of the contact event. Following this contact tracing effort, the World Health Organization considered further transmission of the virus within the United Kingdom to be of "minimal" risk. Contact tracing was extended to Scotland on 14 May according to Public Health Scotland. A "small number" of people in Scotland were ordered to self-isolate following close contact with the person initially reported to have been infected, although overall risk to the general public remained "very low".
On 12 May two new cases of mpox were confirmed by the UK Health Security Agency, both in London, living together in the same household, with no known link between either of them and either the index case or travel to endemic regions. One of the new cases was hospitalised at St Mary's Hospital, while the other case with milder symptoms was said to be self-isolating at home. On 17 May, another four cases of mpox were confirmed by the UKHSA in three Londoners and a person in North East England who had previously travelled to London.
Unusually, none of these new cases had any known contact history with the previous three confirmed cases, which suggested a kind of transmission that had not been seen before, a wider community transmission of the virus in the London area. The UKHSA stated that the risk to the general public remained "very low". Patients with active mpox infection were confirmed to be hospitalised at the Royal Victoria Infirmary in Newcastle upon Tyne and at the Royal Free Hospital and Guy's Hospital in London.
Also on 20 May, UK Health Secretary Sajid Javid reported that another eleven cases had been confirmed, bringing the total in the country to twenty. UKHSA reported on 10 June that 311 of the 314 cases where sex was known were men, and that all of the 151 infected persons who filled out an additional questionnaire and answered questions about sexual practices were men who have sex with men, abbreviated MSM. Dr. Susan Hopkins from the UKHSA urged watchfulness among men who have sex with men. The UK Health Security Agency advised people who have had close contact with a person infected with mpox to self-isolate for 21 days.
Further cases in multiple countries outside the endemic area were reported through the second half of May 2022. On 18 May, Portugal reported 14 cases of mpox. In Spain, there were seven confirmed cases as of 18 May. On the same day, the United States confirmed its first 2022 case of mpox and Canada reported 13 suspected cases.
On 19 May, Sweden, Belgium and Italy confirmed their first cases. On 20 May, Australia, Germany, France and the Netherlands confirmed their first cases. For the remainder of May, multiple European countries and Israel confirmed their first cases. The United Arab Emirates and Mexico also confirmed their first cases.
On 23 May, David Heymann, an advisor for the World Health Organization, said that the likely theory of how the outbreak started is transmission during sexual intercourse of gay and bisexual men at two raves in Belgium and Spain. On 25 May, The Guardian stated that many scientists suspect the disease was circulating across Europe before reaching the MSM community, possibly misdiagnosed or detected only in isolated cases; four cases were diagnosed in 2018 and 2019, all in individuals who recently arrived from Nigeria.
In addition to more common symptoms, such as fever, headache, swollen lymph nodes, and rashes or lesions, some patients have also experienced proctitis, an inflammation of the rectum lining. CDC has also warned clinicians to not rule out mpox in patients with sexually transmitted infections since there have been reports of co-infections with syphilis, gonorrhea, chlamydia, and herpes.