First Case of More Severe Mpox Strain Reported in Sweden

Sweden has announced its first case of the more lethal clade 1 mpox, a variant that has, until now, only been reported in Africa. Mpox, previously known as monkeypox, is caused by viruses categorized into two main branches: clade 1 and clade 2. Clade 2 was responsible for the global mpox emergency in 2022 and 2023, affecting countries like the U.S., the U.K., and Sweden. In contrast, clade 1 viruses lead to more severe illness and higher mortality rates, with cases previously confined to Africa. This is prepared by SSP.

On August 15, the Public Health Agency of Sweden reported detecting a clade 1 virus in a patient who had sought medical treatment in Stockholm. The individual is believed to have contracted the virus during a stay in an African region experiencing a significant mpox clade 1 outbreak. Clade 1 viruses significantly contribute to ongoing mpox outbreaks in countries like the Democratic Republic of Congo (DRC), Burundi, the Central African Republic, and the Republic of Congo. On August 14, the World Health Organization (WHO) declared these outbreaks a global health emergency, highlighting the emerging clade 1b as a particular concern.

The WHO first detected clade 1b in the DRC, and it has since led to infections in African nations where mpox had not been reported before, such as Burundi, Kenya, Rwanda, and Uganda. While Sweden's public health agency did not specify the subtype of clade 1 found in their case, reports indicate that clade 1b has a case-fatality rate of 3% to 6%, whereas clade 1 viruses, in general, can have rates up to 10%. By comparison, the clade 2 viruses responsible for the 2022-2023 outbreak had fatality rates as low as 0.2%.

Swedish officials emphasized that the infection does not increase the risk to the general population, which the European Centre for Disease Prevention and Control (ECDC) currently considers very low. New assessments are expected shortly. Occasionally, imported cases like this one may still occur. If necessary, Sweden has antiviral drugs used to treat similar viruses, such as smallpox, since no specific treatments for mpox are approved. Mpox vaccines can also be used to prevent illness after a known or suspected exposure through a "ring" vaccination strategy, where vaccines are administered to close contacts of an infected person to control the outbreak.

Sweden's state epidemiologist, Magnus Gisslén, reassured that while no additional infection control measures are required at the moment, the situation is being closely monitored, with ongoing assessments for potential new measures. Prior to this, about 300 cases of clade 2 mpox were reported in Sweden, all linked to the 2022-2023 global outbreak.