LONDON — The rising mpox outbreaks in Africa that triggered the World Health Organization’s emergency declaration are largely the result of decades of neglect and the global community’s inability to stop sporadic epidemics among a population with little immunity against the smallpox-related disease, leading African scientists said Tuesday.

Dr. Dimie Ogoina, who chaired the WHO’s mpox emergency committee, said negligence has led to a new, more transmissible version of the virus emerging in countries with few resources to stop outbreaks.

Mpox, previously known as monkeypox, had been spreading mostly undetected for years in Nigeria and elsewhere before the disease had a 2022 outbreak in more than 70 countries, Ogoina said at a virtual news conference.

“What we are witnessing in Africa now is different from the global outbreak in 2022,” he said. While that outbreak was overwhelmingly focused in gay and bisexual men, mpox in Africa is now being spread via sexual transmission as well as through close contact among children, pregnant women and other vulnerable groups.

And while most people older than 50 were likely vaccinated against smallpox — which may provide some protection against mpox — that is not the case for Africa’s mostly young population, who Ogoina said were mostly susceptible.

Mpox belongs to the same family of viruses as smallpox but causes milder symptoms, like fever and body aches. It mostly spreads through skin-to-skin contact, including sex. People with more serious cases can develop prominent blisters on the face, hands, chest and genitals.

Earlier this month, the WHO declared the surging mpox outbreaks in Congo and 11 other countries in Africa to be a global emergency.

On Tuesday, the Africa Centers for Disease Control and Prevention said there were 22,863 mpox cases and 622 deaths on the continent and that infections had jumped 200% in the past week. The majority of cases and deaths are in Congo, where most mpox infections are in children younger than 15.

Africa had nearly 4,000 reported in the past week, said Dr. Jean Kaseya, head of the Africa Centers for Disease Control and Prevention.

About 380,000 doses of mpox vaccines have been promised by Western partners, such as the European Union and the United States, he said. That’s less than 15% of the doses authorities have said are needed to end the mpox outbreaks in Congo, the epicenter of the global emergency.

Dr. Placide Mbala-Kingebeni, a Congolese scientist who helped identify the newest version of mpox, said tests being used in the country did not always pick it up, making it hard to track the variant’s spread.

In May, Mbala-Kingebeni, who heads a lab at Congo’s National Institute for Biomedical Research, published research showing a new form of mpox that may be less deadly but more transmissible. The mutations suggested it was “more adapted to human transmission,” he said, but the lack of tests complicated efforts to monitor outbreaks.

The new variant has been detected in four other African countries as well as Sweden, where health officials said they have identified the first case of a person this month with the more infectious form of mpox. The person had been infected during a stay in Africa.

The WHO said available data does not suggest that the new form of mpox is more dangerous, but research is ongoing.

Marion Koopmans, a virologist at Erasmus Medical Centre in the Netherlands studying mpox, said scientists are now seeing some significant impacts of the disease, noting that pregnant women were miscarrying and some babies were being born infected with mpox.

Ogoina said: “It’s very, very unfortunate that we have had mpox for 54 years and we are only now thinking about therapeutics.”