The country hardest hit by mpox, the Democratic Republic of the Congo (DRC), has had only a trickle of vaccine doses to fight the outbreak across a geographically vast territory that is home to 100 million people. A new analysis by researchers at the World Health Organization (WHO) shows it was also hampered by a scattershot use of that limited vaccine supply.
I call it the confetti strategy: You distribute a little bit everywhere, says Ana Maria Henao-Restrepo, a WHO vaccine specialist who led the analysis. The possibility of having an impact is diminished substantially. She has presented the findings at recent WHO meetings and shared the slides with ScienceInsider. Although the country has managed to vaccinate more than 700,000 people since October 2024, the WHO analysis suggests it has made little difference.
Misaki Wayengera, a geneticist in neighboring Uganda, which is battling its first ever outbreak of the debilitating disease, says he loves this analysis. It gives us the first really intensive, scientifically well-designed assessment of the impact of an mpox vaccination program in Africa, says Wayengera, who advises his governments health ministry about epidemics.
The DRC had the worlds first documented case of mpox in 1976, and for decades it had sporadic outbreaks that died out within months and did not reach beyond remote areas. But in June 2024, a novel strain of the monkeypox virus that causes the disease was rapidly spreading through the eastern part of the country, jumping borders to Uganda and other neighbors. The country approved the use of an mpox vaccine, but it would take another 5 months for doses donated from abroad to arrive.
Supplies were always tight, and an mpox plan for Africa issued in September 2024 by WHO and the Africa Centres for Disease Control and Prevention said the first doses should go to populations at highest risk, which mainly meant contacts of known cases. This strategy creates a ring of immunity around each case to prevent spread of the virus. Ring vaccination was key to the success of the global vaccine campaign that eradicated smallpox nearly 50 years ago. Wayengera agreed that African countries battling mpox should use the same strategy, as he argued in a commentary published in the December 2024 issue of The Lancet Global Health .
But the DRC and other African countries have limited ability to do the surveillance needed to confirm cases and identify their contactscritical components of a ring vaccination campaign. Mpox symptoms are easy to confuse with chickenpox, and in much of the DRC, confirming an mpox case is almost impossible for us because there are provinces that do not have laboratories, says Nanou Yanga, who helps lead the vaccination efforts for the DRCs health ministry. The country also lacks the funds needed to quickly geolocate cases, she adds, which helps guide where to offer vaccination. The incursion of a rebel group into cities and towns in the eastern DRC has added an extra burden in the region, leading many mpox treatment centers to close and large populations to relocate.
To assess the impact of the DRCs vaccination efforts, the WHO scientists, working with the DRC ministry of health, looked at the city of Kinshasa, which has a population of 17 million and by early March had distributed about 500,000 vaccine doses. The researchers geolocated all of the confirmed cases in the city for 2 months after the vaccination campaign took place. They saw cases decline in some areas and increase in others, regardless of which had received vaccines. You cannot really see any patterns or trends, Henao-Restrepo says.
One reason the vaccine appears to have had little effect is that transmission in Kinshasawhich at first was largely driven by sex workers and their clientspeaked in August 2024, long before the vaccine became available. By the time it arrived, there was likely a buildup of natural immunity in the highest-risk populations, says Olivier le Polain, a disease modeler who heads an epidemiology and analytics division at WHO and worked on the analysis.
Ring vaccination campaigns must closely follow the epidemiology of an outbreak, says Henao-Restrepo, who has helped the DRC conduct successful ring vaccination efforts against Ebola outbreaks. The best approach is to focus on areas where the transmission is still going up, she says. You have to have the love and the dedication to look at the detailed data if you really want to beat the virus.
Henao-Restrepo acknowledges the challenges of tracking mpox cases. But she says vaccination campaigns must try to be more aggressive in reaching contacts of those infected. We have to be faster with the vaccination and more targeted to ensure that we really change the trajectory of the outbreak, she says. (New funding recently in from Gavi, the Vaccine Alliance, is now shoring up case tracking, Yanga says.)
Wayengera agrees that moving quickly is key. Genetic analyses show that the Uganda outbreak traces to a novel monkeypox variant that surfaced in September 2023 in Kamituga, a mining town in the eastern DRC. It took almost a year for us to really begin to think about getting vaccine to DRC, he says. By the time we got in, transmission had already exploded. If we had acted in Kamituga area just at [the] time of onset of this outbreak, we would have put out the fire.
Ugandas own vaccination campaign, launched in in January, has had some success containing spread among sex workers and their clients, Wayengera says. But despite the more than 100,000 doses of vaccine donated to the country the outbreak is far from over. Like the DRC, Uganda has struggled to trace contacts and conduct ring vaccination. Sex workers dont keep records of what they do, and if you ask who at end of the day were your contacts, its very difficult to map this out, he says. The virus, as in the eastern DRC, has also spread widely through nonsexual contactwhich is more difficult to trackaffecting many children.
If African countries can intensify surveillance and obtain more doses of vaccine, Wayengera is confident that ring vaccination combined with campaigns that have a broader reach can have a major impact against mpoxs spread. I dont think the opportunity is lost, he says. Do we have the resources to widen the net beyond the epicenters of the disease outbreaks? These are the issues we are trying to fight with here.
