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While Mpox is no longer classified as a PHEIC (Public Health Emergency of International Concern) by the WHO - the recently emerged clade Ib continues to make inroads around the globe - and we are watching for further signs of a recombinant strain which has turned up twice; in travelers to the UK and India.Although it hasn't taken off the way that clade II did in the spring of 2022, we continue to see scattered reports - such the following one from the San Francisco Health Department - from around the globe.
Health Alert: San Francisco Reports First Clade I Mpox Case
April 16, 2026
Situational Update
On April 14, 2026, the first clade I mpox case in San Francisco (SF) was confirmed. The case occurred in an unvaccinated adult who was hospitalized and is improving. The individual reported close contact with someone who traveled internationally to an area where clade I mpox is circulating.
Clade I mpox is distinct from clade II mpox. The mpox outbreak in the United States that began in 2022 is due to clade II mpox and has led to 1066 cases in SF as of April 9, 2026. In contrast, an outbreak of clade I mpox in Central and Eastern Africa has been ongoing since 2023, with sporadic travel-associated cases reported in non-endemic countries and increasing reports of locally-acquired clade I mpox in Europe. Over the last two years, 15 clade I mpox cases have been reported in the United States, including 6 in California. Public health officials are monitoring cases to determine if clade I mpox is more severe than clade II mpox in the United States.
Yesterday, Denmark - which announced an imported case a week ago - announced the detection of 3 more cases, including 1 locally acquired infection.
Since the eradication of smallpox in the 1970s, there has been a growing belief that poxviruses are a thing of the past; a near-forgotten relic of the 20th century.
First case of mpox variant infection in Denmark
Last week, the first case of the mpox variant clade 1b was detected in Denmark, and now three more cases have been confirmed. One of the cases was infected in this country, which is the first example of local transmission.
Last edited on April 27, 2026
Statens Serum Institut (SSI) can now confirm that a total of four cases of mpox clade 1b have been detected in Denmark. In one of these cases, the infection occurred here in the capital area, without prior travel abroad.
Preliminary analyses indicate that there are several independent cases of infection with a common geographical origin outside Denmark.
"It is not unexpected that we are now also seeing local infection in Denmark. Experience from other European countries shows that the infection can spread locally once the variant is introduced," says department head Uffe Vest Schneider from SSI and continues:
"At the same time, it is important to emphasize that the course of the disease has so far been mild, and that the overall risk in the population remains low."
Following the situation closely
In the past year, a number of European countries and countries outside Europe have reported cases of mpox clade 1b with local spread of infection.
Those infected in Denmark have so far had mild illness, and the health authorities continue to assess that there is no cause for concern among the population.
The Danish National Board of Health, the Danish Patient Safety Agency and the State Serum Institut are closely monitoring the situation and collaborating with clinical environments and relevant organizations to track down infection, limit further spread and inform relevant target groups.
At the same time, the importance of vaccination and contraception is emphasized in groups where there is an increased risk of infection.
Also yesterday, the State of Hawaii, Department of Health published the following report on the first detection of clade Ib in wastewater on the island of Oahu.
MPOX DETECTED AT WASTEWATER SAMPLING SITE ON OʻAHUPosted on Apr 27, 2026 in Newsroom
HONOLULU — The Hawai‘i Department of Health (DOH) is reporting a wastewater sample from O‘ahu that has tested positive for clade I mpox. The sample was collected on April 13, 2026, from a wastewater treatment facility on Joint Base Pearl Harbor Hickam (JBPHH). This is the first time clade I mpox has been detected in wastewater in Hawaiʻi. To date, no clinical case of clade I mpox has been identified in Hawai‘i.
At this time, the risk for the general public is low. The presence of clade I mpox virus in wastewater does not confirm a clinical case or community spread. Instead, it serves as an indicator to be alert for possible mpox cases. People at higher risk of mpox infection should consider being vaccinated with two doses of the JYNNEOS (mpox) vaccine if not already protected.
The JBPHH facility serves not only on-base military housing and facilities, but public sites that receive large numbers of residents and visitors, including the Pearl Harbor National Memorial Museum.
DOH was notified of the initial detection on April 20, 2026, with positive confirmatory results received on April 24, 2026. Subclade analysis was undetermined due to sample degradation. A subsequent sample, collected on April 20 from the same wastewater facility, has tested negative for mpox. Major civilian wastewater facilities on O‘ahu are routinely tested for clade I mpox, and all samples have tested negative as of April 22, 2026.
Clades are genetically distinct groups, or lineages, of a virus that develop as it evolves over time. There are two types of the virus that causes mpox, clade I and clade II. Both types spread the same way and can be prevented using the same methods. A clade II mpox outbreak in the United States that began in 2022 has led to 65 cases in Hawaiʻi as of April 20, 2026. There has been an ongoing outbreak of clade I mpox since 2023 in Central and Eastern Africa, with recent community transmission in Western Europe. To date, clade I cases in the continental U.S. have been among people who had recently traveled to countries with ongoing outbreaks. So far, there has not been sustained transmission of clade I mpox reported in the U.S. Public health officials are monitoring cases to determine if clade I mpox is more severe than clade II mpox in the U.S.
DOH encourages anyone who has recently traveled to an area with active transmission, or who has been in close contact with a symptomatic individual, to monitor their health and consult with a healthcare provider regarding potential risks. People with mpox often get a rash and may have other symptoms like fever, chills and swollen lymph nodes. The rash, which typically begins as bumps and progresses to blisters and pustules, may be located on the hands, feet, chest, face, or mouth, or near the genitals. If you develop symptoms or believe you are at high risk, contact your healthcare provider to discuss testing and vaccination.
Since the eradication of smallpox in the 1970s, there has been a growing belief that poxviruses are a thing of the past; a near-forgotten relic of the 20th century.
But a 2020 report in the Bulletin of the World Health Organization warned that our waning immunity to smallpox puts society at increasing risk of seeing new poxvirus epidemics (see WHO: Modelling Human-to-Human Transmission of Monkeypox).
The emergence and international spread of 2 new Mpox clades (Ib & IIb) since 2020 - and a new recombinant recently reported in Asia - would seem to reinforce that warning.
Some recent blogs on Mpox research include:
Eurosurveillance: Waning Humoral Immunity Following Monkeypox Virus Infection and Vaccination, Canada, 2020 to 2023
The UK Recombinant Mpox Case: Reactions from the UK Science Media Centre
WHO DON: Broader Transmission of Mpox Due to clade Ib MPXV – Global situation
