On August 14, the World Health Organization declared a growing outbreak of mpox in the Democratic Republic of the Congo (DRC) and other African countries a global health emergency of international concern. The alert marks the second time in three years that an international health emergency has been declared due to the rapid spread of the disease formerly known as monkeypox. The last mpox emergency designation was in July 2022, when an outbreak extended across 116 countries, impacting nearly 100,000 people, and killing about 200.
In the latest outbreak, more than 15,000 confirmed and suspected cases of mpox have been reported in Central and Western Africa along with 537 deaths, making the new outbreak deadlier than the one two years ago. Yale epidemiologist Chantal Vogels, PhD, has been studying mpox; and she led a team that developed novel genome sequencing approaches for viruses such as mpox to better investigate how they emerge and spread. An Assistant Professor of Epidemiology (Microbial Diseases) at the Yale School of Public Health, Vogels recently took a moment to share her thoughts on the latest mpox outbreak.
How is the current mpox outbreak different from the one two years ago and why is it more deadly?
CV: The monkeypox virus that causes mpox consists of two genetically distinct clades, named clades I and II. In phylogenetics, a clade is a distinct group of organisms that is believed to have evolved from a common ancestor. So, in this case you might think of clades I and II as two main branches extending off the monkeypox virus evolutionary tree. Historically, clade I has circulated in Central Africa (mainly in the DRC) and clade II has circulated mainly in West Africa. Of these two clades, clade I has been associated with more severe disease and substantial mortality (up to 11% of those infected), whereas clade II is typically associated with milder infections. The 2022 global outbreak was caused by an offshoot or variant of clade II called clade IIb, which was mainly transmitted through direct human-to-human transmission, particularly through sexual contact among men who have sex with men. The current outbreak is mainly being driven by clade I viruses, including a new clade Ib virus that was found in a mining region of South Kivu in eastern DRC and that likely emerged around the fall of 2023. Historically, transmission of clade I viruses has been linked to zoonotic spillover events (transmission of a virus from one species to another such as from animals to humans) with limited secondary transmission from human-to-human. What is concerning about the current outbreak is that it is a clade I virus associated with direct human-to-human transmission. This indicates the monkeypox clade 1 virus may have evolved to propagate human-to-human transmission and infection more efficiently.
Children and women appear to be more susceptible to this new version of the virus; can you explain why?
CV: The current mpox outbreak is complex and more genomic studies are needed to better understand the situation. Evidence is emerging that suggests the current outbreak is caused by both clade Ia and Ib viruses. In South Kivu, clade Ib was linked to sexual transmission, disproportionally affecting women who identify as sex workers. However, the increased number of cases reported in other parts of DRC may be the result of independent spillover events of clade Ia viruses and may not be due to a single human outbreak. These spillover events together with secondary household and community transmission may explain the increased number of cases reported among children, but further studies are needed to confirm this.
Is the current mpox outbreak in Africa a potential concern for other countries and if so, what should people do to protect themselves?
CV: The current mpox clade I outbreak is of international concern. What is particularly worrying is the extremely high number of cases and the rapid spread to surrounding countries, where cases have never been reported before. This shows how quickly the virus can emerge into new regions, which is likely facilitated by direct human-to-human transmission and human movement. Vaccination and public awareness were key in mitigating the 2022 mpox clade IIb outbreak, and it is critical that vaccines now become accessible in places where they are needed most, particularly in DRC and other parts of Africa.