What are the risks of mpox spreading around the world again, two years after the epidemic that caused the death of 140 people and some 90,000 cases in over 75 countries? Experts are beginning to ask this question, as on Wednesday, August 14, the World Health Organization (WHO) declared the ongoing mpox epidemic in the Democratic Republic of Congo (DRC) and more than a dozen other African countries to be a public health emergency of international concern (PHEIC), the UN organization's highest alert level.

These concerns are fueled by the fact that the epidemic, which has continued in the DRC for two years, has skyrocketed since the beginning of the year, and that a new clade, in other words a new viral strain, began circulating in September 2023 in the east of the country, recently spreading to several neighboring countries that had never encountered the virus on their territory.

On Thursday, a case of this new, more virulent clade 1b was identified for the first time outside Africa: A person living in the Stockholm area of Sweden was diagnosed on his return from Africa. "There are likely to be further imported cases of Clade 1 in the European region over the coming days and weeks," commented the WHO's European branch on Thursday.

For its part, the European Centre for Disease Prevention and Control raised its risk level on Friday:  "Due to the close links between Europe and Africa, we must be prepared for more imported clade I cases."

But the alarm has also been sounded outside Europe. On Friday, Pakistan announced that it had identified its first case of mpox in a traveler returning from a Gulf country. The clade involved was not yet known.

So, are we about to experience the scenario of the 2022 epidemic? For Xavier Lescure, an infectious diseases specialist at Bichat Hospital, "2022 was the trial run for a zoonosis [a disease that passes from animals to humans] linked to man-made environmental disturbances." In his opinion, "we're going to have a harder time circumscribing viral circulation than we did in 2022, because it's spreading from a wider area and is not limited to a particular population; all with a more virulent clade."

Let's go back two years. The outbreak outside Africa was carried by clade 2b, a variant of the clade circulating in West Africa, known to be less lethal than clade 1, which dominates the Congo Basin in the center of the continent. As a result, despite widespread distribution in Europe and the Americas, the case-fatality rate remained below 1%. The disease had spread from a single case of an infected person returning from Nigeria, and had circulated mainly among men who have sex with men (MSM), a community highly aware of sexual health issues since the AIDS pandemic, and which had managed to take action rapidly to limit contamination.

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