Epidemic risks, treatments, vaccine effectiveness… Mpox: experts take stock of the situation

Le Mpox fait des ravages en Afrique et inquiète la communauté internationale. EPA – SHAHZAIB AKBER

The European Union delivered this Thursday, September 5, to the Democratic Republic of Congo a first batch of 99,000 doses of vaccines against Mpox, in a country where the epidemic is wreaking havoc: more than 19,000 cases and 650 deaths since the beginning of the year. Scientists from ANRS Emerging Infectious Diseases, an offshoot of Inserm, and IRD reassure about the risk of an epidemic in France, even if many unknowns remain.

“A lot of nonsense has been said about Covid, but I don't think there is any reason to worry. There are treatments, vaccines… and for the past two years, we have had time to mark out the care circuit”: Éric d’Ortenzio, physician, epidemiologist and head of the strategy and partnerships department at ANRS Emerging Infectious Diseases (MIE), wanted to be rather reassuring about the risk of an Mpox epidemic in France, this Thursday, September 5, during a press conference organized the day after the announcements by the Ministry of Health aimed at strengthening the vaccination strategy.

Vaccine effectiveness, treatments, progress of the epidemic, situation in Africa and Europe, scientists from ANRS-MIE and IRD took stock of the situation, while the first doses of vaccine arrived that same day in the Democratic Republic of Congo, the epicentre of the epidemic affecting several African countries, including Burundi, Congo-Brazzaville and the Central African Republic.

The epidemic “mainly in Africa”

“The epidemic is mainly located in the Democratic Republic of Congo and neighboring countries", it is linked to the circulation of the virus of clade (which can be translated as "strain") 1b of the virus, underlines Professor Yazdan Yazdanpanah, at ANRS-MIE.

On August 14, the head of the World Health Organization (WHO), Dr. Tedros Adhanom Ghebreyesus, declared "a public health emergency of international concern" in the face of the surge in the number of cases in Africa,“The number of cases reported so far this year has already surpassed last year's total, with more than 15,600 cases and 537 deaths”, WHO said.

“We have more than 19,000 cases and 650 deaths this year”, said Dr Placide Mbala, head of the epidemiology and global health department and head of the pathogen genomics laboratory at the National Institute of Biomedical Research Institute (INRB) in the DRC, with extensive experience with Mpox: “Mpox has existed in the DRC for over 50 years, but the disease has always remained confined to forest regions”.

Mode of transmission, clades, risks, situations differ depending on the country, one year after the appearance of clade 1b, identified in 2023, while the year 2022 saw the emergence, mainly in Nigeria, of clade 2, and caused a first global epidemic. It is clade 2 that circulates almost exclusively in Europe and France, with no deaths to date: “Since January 1, 2024, a total of 143 cases of clade 2 Mpox infection have been reported to Public Health France, including 14 in the last seven days”, indicates SPF in a press release published this Thursday.

France wants to “prevent the emergence of clade 1b” on its territory, “in accordance with the opinion of the High Authority of Health” (HAS) of September 2, 2024. To date, a single case of Mpox 1b has been identified in Europe, in Sweden. There is also a case in Thailand, and investigations are ongoing.

Clade 1 or clade 2, the distinction is not trivial: viruses are not equally contagious and dangerous. “Mortality varies from 3.5% to 6.8% for the 1a”, specifies Placide Mbala.

Vaccination imminent in Africa, recommended for at-risk groups in France

It will take a few weeks to organize the vaccination, which should start next month in the DRC. “A vaccination plan has been put in place. Health workers, sex workers, MSM, men who have sex with men, transgender people, and children aged 1 to 17”, on the front line (four deaths out of five), are a priority, says Placide Mbala. Veterinarians and hunters, in contact with animals, also.

Protection is essential because “the epidemic has changed” face, recalls Martine Peeters, research director at the IRD in Montpellier: it was a zoonosis (transmission from humans to animals), it has become a disease transmissible from humans to humans. Today, several epidemics overlap.

In France, “People targeted by preventive vaccination are men who have sex with men reporting multiple partners, transgender people reporting multiple partners, people in prostitution and sex workers, professionals in places of sexual consumption”.

If the disease “looks like smallpox, with fever, rash and very painful lesions, particularly on the mucous membranes”, Professor Xavier Lescure, Inserm researcher and doctor in the infectious and tropical diseases department at Bichat Hospital, recalls the risk of complications: “Bacterial superinfections that can affect eyes, severe forms with encephalitis and myocarditis, dehydration of toddlers.

Children and immunocompromised people are on the front line.

Trials are underway.

“The currently authorized vaccine was developed to prevent smallpox. Repositioned on Mpox, it increased its effectiveness, and I am not sure that a vaccine specific to Mpox should be developed”, specifies Dr. Liem Binh Luong Nguyen, infectious disease specialist at the clinical investigation center of vaccinology at Cochin Hospital. According to him, “the rate of neutralizing antibodies that prevent the virus from multiplying, drops quite quickly after a year”. He recommends “to get vaccinated every two years", "it’s not dangerous". But "many at-risk people haven’t been vaccinated".

"Effective treatments"

"Treatments save lives, it is crucial that patients know about it", insists Professor Alexandra Calmy, infectious disease specialist and head of the HIV/AIDS unit at the Geneva University Hospitals.

An antiviral used against smallpox, tecovirimat, is on the front line. It remains to be seen whether it “should be combined with other treatments” for greater effectiveness.

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“The monkey is not considered a reservoir host of the virus, rodents are more likely”, says Eric d’Ortenzio.

This is not the only mystery to be solved for researchers: “Little is known about the characteristics of the virus”, adds Martine Peeters from Montpellier, who worked with Placide Mbala on “samples from 600 symptomatic patients” from the DRC, in 2023, “more than 80% of clade 1a strains”.

On the mode of transmission: “Respiratory transmissions are very marginal”, insists Xavier Lescure, who also remains unclear on the transmission routes among sex workers and in the homosexual community: “We do not know if it is only sexual relations, or because of skin-to-skin”.