Mpox Outbreak 2023

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Last reviewed
December 5, 2023
Content Overview
Mpox outbreaks in 2023 include Africa, the Americas, China, France, Japan, London, New York, Portugal, South Korea, Spain, Taiwan.

Mpox Outbreaks

The World Health Organization (WHO) Mpox External Situation Report #30 confirmed on November 25, 2023, that it has received mpox case reports from 115 affected countries since May 2022. Since January 2023, over 12,000 suspected mpox cases and 581 related deaths (case fatality ratio 4.6%) have been reported. During October 2023, 668 new laboratory-confirmed cases were reported from 29 countries. The most affected regions were the Western Pacific and European regions. Based on the data, the mpox virus (MPXV) outbreak continues at a low transmission level in the European Region and the Region of the Americas. Overall, the global risk for men who have sex with men and sex workers is assessed as moderate, says the WHO. The WHO Director-General declared a public health emergency of international concern (PHEIC) regarding outbreaks on July 23, 2022. The WHO announced the PHEIC ended on May 11, 2023. The natural reservoir of the zoonotic mpoxvirus remains unknown.

Mpox Virus Cades

There are two MPXV clades: clade I, previously known as the Congo Basin clade, and clade II, formerly the West African clade; clade II further has two subclades: clade IIa and clade IIb. Since May 2022, an epidemic of clade IIb MPXV was initially detected in the Canary Islands and is ongoing globally in 2023. Separately, clade I MPXV community outbreaks occur regularly in Cameroon, the Central African Republic, and the Democratic Republic of Congo (DRC). The European Centre for Disease Prevention and Control (ECDC) stated on December 5, 2023, that there's no evidence that clade 1 is spreading outside of central Africa. Before April 2023, no formally documented cases of sexual transmission of clade I MPXV were registered globally. 

Mpox United States 2023

In the U.S., initial mpox virus clade IIb cases were detected in Boston, MA, in May 2022. The U.S. government declared an outbreak in August 2022. The mpox public health emergency in San Francisco, CA, ended on October 27, 2022, followed by New York in November 2022. On June 20, 2023, NYSDOH Commissioner James McDonald posted a Mpox Update video. On January 31, 2023, the U.S. HHS did not renew the public health emergency declaration for mpox.

As of October 26, 2023, the U.S. Centers for Disease Control and Prevention (CDC) confirmed 31,010 mpox cases and 55 related deaths. The CDC  published a Dispatch, Volume 29, Number 10—October 2023, confirming that 1.3% of reported mpox instances were in children and adolescents <18 years of age. The analysis of global surveillance data showed one hospital intensive care unit admission and 0 deaths in that age group.

U.S. Mpox Wastewater Data was last updated on November 29, 2023.

Mpox Transmission

A study published on November 8, 2023, reported that sexually transmitted infections could facilitate mpox transmission in Chicago, Illinois. And in a CDC Morbidity and Mortality Weekly Report published on September 1, 2023, among 38 (73%) patients with no known exposure to a person with mpox, behaviors preceding illness included sexual activity (17; 45%), close face-to-face contact (14; 37%), attending large social gatherings (11; 29%), and being in occupational settings (10; 26%). The Lancet reported on August 4, 2023, that sexually transmitted coinfections (STI) were prevalent in mpox patients, including gonorrhea (28%), chlamydia (25%), syphilis (8%), and HIV (38%).

The U.S. CDC Advisory Committee on Immunization Practices (ACIP) presented various mpox data on June 23, 2023. The ACIP presentation on October 25, 2023, reviewed mpox infections in Chicago, indicating an increase in mpox (18), particularly among previously JYNNEOS vaccinated persons. The Notes from the Field and the MMWR Domestic Mpox Response — U.S., 2022–2023, published on May 19, 2023, disclosed Black and Hispanic persons represented 33% and 31% of cases, respectively; 87% of 42 fatal cases occurred in Black persons. The CDC's Clinician Outreach and Communication Activity call on May 18, 2023, presented Mpox Update: Stay Up to Date on Testing, Treatment, and Vaccination. Furthermore, the CDC issued a Health Update on May 15, 2023, regarding Mpox vaccination breakthrough cases, and the CDC disclosed Mpox wastewater detections and Non-Variola Orthopoxvirus Laboratory Testing. As of November 2023, Wastewater Scan publishes an updated map of mpox detections.

A study published on August 9, 2023, concluded individuals without visibly prominent mpox symptoms transmit the mpox virus.

Mpox Africa

The WHO reports that mpox is an infectious disease endemic in densely forested West, Central, and East Africa regions. The first human case of Mpox was identified in the Democratic Republic of Congo (DRC) in 1970. During 2016–2022, PCR testing confirmed 100 mpox cases among 302 suspected cases in the Central African Republic. The WHO published a Disease Outbreak News in November 2023, outlining the ongoing and evolving epidemiology of mpox in the DRC. This summary highlights the reporting since January 2023 of 12,569 suspected cases in 156 health zones from 22 out of 26 provinces, and among these, 581 deaths (case fatality ratio 4.6%). Newly identified outbreaks related to sexual transmission of clade I MPXV are also reported in the DRC. The CDC issued Level 1 travel advisories in 2021 to alert international travelers regarding mpox outbreaks in African countries.

Mpox Europe

The European Centre for Disease Prevention and Control (ECDC) published a communicable disease threats report for week #27, indicating a mpox outbreak in Portugal as of early July 2023. The ECDC published a report on public health considerations for mpox in EU/EEA countries in 2023. In addition, a study published by the International Journal of Infectious Diseases on May 15, 2023, shows considerably more mpox DNA in wastewater samples than expected based on hospitalization data, suggesting the mpox outbreak was underestimated in central Europe.   Public Health France reported 17 confirmed mpox cases in the Centre-Val de Loire region in April 2023. According to researchers from Portugal's National Institute of Health, a genomic and epidemiologic analysis of the 2022 mpox outbreak estimates that 1.3% of MSM in Portugal were infected with the virus. According to the Carlos III Health Institute, six cases of mpox were diagnosed in Spain in May 2023, 56 since the beginning of 2023, and 7,555 since the mpox outbreak began in May 2022. The Vall d'Hebron (Barcelona, vaccinated against smallpox in childhood) and Ramón y Cajal (Madrid) hospitals diagnosed two patients in May 2023 who had already had the infection before.

Mpox Pacific Region

China's National Health Commission (NHC) confirmed in a statement in September 2023 that it plans to manage mpox, Category B protocols, similar to other infectious diseases such as COVID-19, HIV, and rabies, after detecting 501 cases of viral infection in August 2023. These reported cases have been identified as clade IIb MPXV. The WHO situation report #27, published on August 14, 2023, identified sustained community transmission of mpox in China. Mpox cases increased to 491 on the Chinese mainland in July 2023, according to China's Center for Disease Control and Prevention (China CDC). That was an increase from 106 cases in June 2023. Since June 23, 2022, China has listed mpox as a second-class legal infectious disease. The WHO reported 106 mpox cases in Beijing in July 2023, plus recent infections in Taiwan and Hong Kong. The Hong Kong Special Administrative Region of the People's Republic of China recently recorded its fifth Mpox patient since September 2022. The Taiwan Centers for Disease Control and Prevention reported that 266 cases (250 local and 16 imported cases) have been diagnosed in Taiwan. As of August 7, a total of 77,809 mpox vaccination services have been completed in China.

A U.S. CDC study reported in July 2023 that asymptomatic mpox infections were likely underestimated in Japan and were comparable in magnitude to symptomatic infections. Japan's Ministry of Health, Labor and Welfare Health reported 169 mpox cases as of May 28, 2023, since the first domestic case in July 2022. On March 20, 2023, the Japanese Ministry of Health reported 13 men were confirmed to have a mpox infection. The Western Pacific Region reported additional mpox cases in early April 2023, driven by an outbreak of mpox affecting mainly men in Japan. 

The Korean Herald reported that Korea's Centers for Disease Control and Prevention announced in April 2023 that it would raise the crisis alert level from 'Level 1' to 'Level 2 caution' following a mpox outbreak of about sixty cases.

Mpox United Kingdom

The U.K. Health Services Agency (UKHSA) began reporting mpox cases in March 2022, which accelerated in May 2022. The first smallpox specimen was identified during this outbreak through retrospective testing in the United Kingdom on March 7, 2022. The earliest date of smallpox symptom onset in the U.K. was reported as April 17, 2022. By December 2022, 3,732 confirmed and highly probable mpox cases were reported in the U.K.; over 3,000 were in London, England. Between January and October 31, 2023, a total of 88 mpox cases have been detected in the U.K., with at least 41% of these cases reported to have been acquired outside the U.K.

Targeted pre-exposure vaccination commenced in June 2022, with over 78,000 first doses and over 43,000 second doses given by November 2023. The JCVI advises that pre-exposure vaccination should target GBMSM who are at the highest risk of exposure to mpox, to be identified via sexual health services using markers of high-risk behavior similar to those used to assess eligibility for HIV pre-exposure prophylaxis (PrEP) but applied regardless of HIV status. On June 16, 2023, the UKHSA announced that mpox vaccinations would remain available in London. The UKHSA published that the mpox clade of monkeypox predominantly circulating in the U.K. (Clade IIb, B.1 lineage) was no longer classified as a High Consequence of Infectious Disease. Before the recent outbreak, between 2018 and 2021, there were seven cases of mpox in the U.K. Of these; four were imported. There was no documented community transmission in previous outbreaks.

Mpox in Women

Eurosurveillance published a study on December 1, 2022, on mpox infections in 158 women. In Spain, 7,393 confirmed cases of Mpox, 2.1% of cases (158) have been in women diagnosed between April 26 and Nov 21, 2022. The average age of female patients was 34 years, and two were pregnant at the time of mpox infection. The most likely transmission mechanism was close contact during sexual relationships. 

Mpox and HIV

People with HIV and mpox were not at an increased risk for hospitalization unless they were immunosuppressed, according to an abstract presented at the International AIDS Society Conference on HIV Science in July 2023.

Mpox Disease

The mpox virus, a member of the Orthopoxvirus genus in the family Poxviridae, causes mpox. The mpox virus has identified two distinct genetic clades of the Congo Basin and the West African clades. According to the WHO, the mpox virus is transmitted from one person to another by contact with lesions, body fluids, respiratory droplets, and contaminated material. A meta-study published in the Archives of Virology on June 29, 2023, found that the median mpox incubation period is seven days, and immunocompromised people with HIV comprise about 36% of documented cases.

Mpox Vaccines and Treatments

Various mpox vaccines (JYNNEOS®) and treatments (TPOXX) are authorized in 2023. Numerous research studies have clinically reviewed the mpox outbreak as of September 2023.