Mpox Clade 1b Outbreak: The Global Health Response Is Still Being Tested

The World Health Organization's decision on 14 August 2024 to declare mpox clade 1b a public health emergency of international concern was the second time in two years that the agency had applied its highest alert to the same disease. The earlier emergency, declared in July 2022 for the global clade IIb outbreak, was lifted in May 2023 after cases fell in most countries. This time the geography was different. The new strain had been spreading for months in the eastern Democratic Republic of the Congo before crossing into Burundi, Kenya, Rwanda and Uganda, and the Africa Centres for Disease Control and Prevention had declared its own first-ever Public Health Emergency of Continental Security one day earlier, on 13 August 2024.

Mpox, formerly called monkeypox, is caused by the monkeypox virus, an orthopoxvirus related to smallpox. The virus has two broad genetic families: clade I, long associated with Central Africa and more severe disease, and clade II, long associated with West Africa. The 2022 global outbreak was driven by clade IIb. Clade 1b is a distinct offshoot of clade I and was identified in South Kivu province, where researchers began documenting sustained human-to-human transmission through close contact, including sexual contact, in early 2024.

The emergency is not a single outbreak

What the world now calls the clade 1b emergency is better understood as two overlapping epidemics under one name. In the Democratic Republic of the Congo, clade Ia has circulated for years in rural, forested areas, often moving from animals to humans and then through households. The newer clade 1b pattern is urban and mobile: it spread through the mining town of Kamituga in South Kivu, then followed trucking routes and cross-border trade. It appeared in Burundi and other countries that had never previously reported mpox.

Sweden's public health agency confirmed the first known clade 1b case outside Africa on 15 August 2024, in a person who had travelled from an affected area. Thailand reported a case days later. Each detection outside the continent set off the same debate: whether a single imported case warranted entry screening or border closures. The separate question was whether travel advice should change. The World Health Organization did not recommend restrictions, and the European Centre for Disease Prevention and Control kept the risk to the general European population low. It does not follow, however, that because broad travel bans are poorly calibrated, the international concern is misplaced. The emergency declaration is primarily about moving vaccine and diagnostic resources into places where transmission is happening now.

The response architecture is being tested again

The WHO's temporary recommendations asked countries to strengthen surveillance and to avoid stigmatising affected groups. They also asked countries to prepare vaccination for contacts and health workers. The agency issued a global strategic preparedness and response plan that called for $135 million over six months. Africa CDC worked with governments to mobilise vaccines and diagnostics. Africa CDC also pushed for better access to antiviral treatment. The difference from 2022 is that this time the disease is not evenly spread across wealthy and poor countries. The burden sits overwhelmingly in the Democratic Republic of the Congo, Burundi, Uganda and neighbouring states, and the pace of the response depends on how quickly vaccines move there.

Bavarian Nordic's MVA-BN vaccine, sold as Jynneos in the United States and Imvanex in Europe, is the most widely available mpox vaccine. Canada markets the same product as Imvamune. Japan's LC16 vaccine has also been offered, particularly for children. Dose donations began arriving in the Democratic Republic of the Congo in September 2024, but the quantities were modest compared with the number of people at risk, and distribution from the capital to the east is slow because of cold-chain requirements and poor roads. Conflict in the eastern provinces makes the last mile more dangerous still.

Vaccines exist; access is the constraint

The central problem is no longer whether a vaccine exists. It is how quickly doses can reach the health zones where clade 1b is circulating, and whether enough countries will pay for the supply chain. Africa CDC has published country-level data on its mpox dashboard, which tracks laboratory-confirmed and suspected cases across the continent. Gavi, the Vaccine Alliance, established a global stockpile and announced that it would make up to 500,000 doses available, while the United States, the European Commission, Japan and others pledged donations. Pledges convert unevenly into delivered doses, and delivered doses are not the same as administered doses.

Several governments have used the emergency to justify entry screening at airports and temperature checks, particularly in Asia and the Middle East. Public health lawyers have warned that such measures can deter people from reporting symptoms and can push transmission into hidden networks. The counterargument is straightforward: when a novel clade with higher case fatality than clade IIb reaches a new region, a cautious response is rational, and some screening is inexpensive. The evidence from the 2022 outbreak, however, suggested that travel measures did not stop clade IIb and added little beyond what testing and contact tracing in the receiving country could achieve. The WHO Director-General's declaration made the same point in plainer language: restrictions should not be the default.

The data problem

Counting cases in the eastern Democratic Republic of the Congo is difficult. Laboratories are limited, transport of samples from remote health zones is slow, and many people with mpox do not seek care in facilities that report to the national surveillance system. Suspected cases outnumber laboratory-confirmed cases by a wide margin, and the case fatality ratio is uncertain. Clade I mpox has historically been associated with a case fatality ratio of around 3 to 10 percent in different settings, but those figures come from studies with incomplete follow-up and are not a fixed property of the clade. Children, pregnant women, and people with untreated HIV or other causes of weakened immunity appear to be at higher risk of severe outcomes.

The uncertainty cuts both ways. It makes the emergency declaration more necessary, because the world cannot manage a threat it has not measured. It also makes public communication harder, because the most alarming historical fatality figures are repeatedly quoted even when current data do not support them. The European Centre for Disease Prevention and Control's risk assessment noted that the available data are too limited to fix a reliable case fatality ratio for clade 1b outside the most heavily studied settings.

Stigma, then and now

In 2022, mpox was initially framed as a disease of men who have sex with men, a framing that shaped public messaging, testing and vaccine eligibility around the world. It protected some at-risk groups while also attaching shame to an infection that spreads through many kinds of close contact. The clade 1b outbreak arrived with a similarly narrow frame. Because sexual transmission was documented early in South Kivu, early reporting called it a sex-linked outbreak, but household transmission, mother-to-child transmission and infection among health workers are also part of the picture.

Researchers and community organisations in Africa have asked that the response fund contact tracing and risk communication in French, Swahili, Lingala and other local languages, not just in English. They also point out that the people most at risk in mining towns and border markets are often mobile and undocumented. Many work informally, which makes them harder to reach through standard health systems. A vaccination campaign that assumes stable addresses and fixed clinics will miss many of the people who need protection first.

What the next months will show

The test of the current emergency is not whether individual countries report imported cases. It is whether the resources that follow a declaration of international concern arrive in time to change the epidemic curve in the affected provinces. That means buying doses at a price the Democratic Republic of the Congo can sustain and paying for the cold chain and the health workers who administer vaccines. It also means building laboratory capacity that survives after the attention moves on.

The precedent being set now matters beyond mpox. When the World Health Organization declares a public health emergency for a disease concentrated in low-income countries, the language of global solidarity is easiest at the start, when television crews are present. The harder question is what remains six months later, after the first donations have been used and the next competing crisis arrives. The answer will be visible in the vaccination registers of South Kivu and Burundi, not in the declarations issued in Geneva.

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