Mpox Outbreak Update: Active Transmission in Uganda, Rwanda, Kenya, Zambia, Republic of Congo, Tanzania, Sierra Leone; Travel-Linked Cases Reported in UK, Germany, India, China, Belgium, Qatar, Thailand, USA, France, UAE, Brazil, Canada, Oman, Sweden, and Switzerland as WHO Gives New Report – Travel And Tour World

Mpox, caused by the monkeypox virus (MPXV), remains a global public health concern with a complex epidemiological profile. As of May 2025, the World Health Organization’s External Situation Report #52 provides an updated and thorough analysis of the multi-country mpox outbreak, highlighting ongoing transmission dynamics, particularly in Africa, and surveillance of travel-related cases globally. This article synthesizes the key findings, scientific data, public health responses, and challenges described in the latest report, offering a detailed picture of the outbreak status and the evolving strategies to control mpox transmission.

Epidemiological Overview

Global Case Counts and Geographic Spread

From January 1, 2022, to March 31, 2025, the global mpox outbreak has recorded 138,029 confirmed cases and 317 deaths across 132 countries. However, much of the transmission burden remains concentrated in African countries, with 19,179 confirmed cases reported in 2024 and 14,758 in early 2025.

The Democratic Republic of the Congo (DRC) is the epicenter in Africa, with over 21,649 cases reported since January 2024, including 1,610 cases in the most recent six weeks (March 10 – April 20, 2025). Other heavily affected countries include Uganda, Sierra Leone, and Burundi. Sierra Leone has experienced a sudden surge in cases during early 2025, reporting over 1,387 confirmed cases and 10 deaths, with over 500 new cases in just one recent week, indicating active community transmission.

In contrast, many countries outside Africa report mpox cases primarily linked to international travel, with few or no sustained community transmissions. This dynamic emphasizes the virus’s ongoing ability to spread via global human mobility.

Virus Clades and Transmission Dynamics

Monkeypox virus is categorized into distinct genetic clades with different epidemiological patterns:

• Clade Ia: Primarily found in the DRC and neighboring Central African countries, where the virus is historically endemic. Transmission mainly occurs through zoonotic spillover (animal-to-human), with some secondary human-to-human spread. Emerging data show increasing sustained human-to-human transmission in urban settings, particularly in Kinshasa.
• Clade Ib: Recently identified in 2023, this clade dominates the current outbreaks in Central and Eastern Africa. Notably, no zoonotic origin has been confirmed for these cases; transmission is predominantly human-to-human, including sexual contact. Clade Ib has been detected in 29 countries, with 10 countries in Africa experiencing community transmission in the past six weeks.
• Clade IIa: Newly reported in West African countries such as Côte d’Ivoire, Ghana, Guinea, and Liberia, clade IIa infections have been documented in both adults and children. The transmission is suspected to involve multiple zoonotic spillover events and limited human-to-human transmission.
• Clade IIb: Responsible for the multi-country outbreak outside Africa starting in 2022, mainly among men who have sex with men (MSM) through sexual contact. While some countries report infections in other populations, these have not resulted in sustained community spread.

Epidemiological Trends in Africa

Democratic Republic of the Congo (DRC)

The DRC remains the country most affected by mpox, with ongoing transmission of both clade Ia and Ib viruses. Recent genomic analyses reveal widespread circulation of clade Ib in 10 provinces and co-circulation with clade Ia in five provinces. The capital, Kinshasa, is a hotspot for sustained human-to-human transmission, with evidence of viral mutations suggesting adaptation.

Weekly surveillance shows that suspected mpox cases remain high, ranging from 2,000 to 3,000 per week since mid-2024. However, confirmed cases show a declining trend since early 2025, likely due to diminished testing capacity rather than a true decrease in incidence. The stable high test positivity rate (~50%) supports this interpretation.

Sub-national data reveal diverse epidemic trajectories: South Kivu province shows a decreasing trend, Tanganyika a recent surge, and other provinces like Sankuru and Tshuapa show rising cases linked to enhanced surveillance efforts. The northwestern historically endemic provinces continue to report many suspected cases.

Uganda

Uganda continues to report a substantial mpox burden with over 4,500 confirmed cases in 2025. Although recent weeks show a downward trend, transmission remains widespread, with approximately 200 new confirmed cases weekly. Vaccination campaigns targeting key populations and frontline workers are underway.

Sierra Leone

Sierra Leone is experiencing a rapid and large mpox outbreak since January 2025, with confirmed cases surpassing 1,300 and a case fatality rate of 0.7%. The Western Area Urban and Rural regions, including the capital Freetown, account for 90% of cases. Transmission appears to be primarily driven by sexual contact in urban settings, supported by demographic data showing even gender distribution and predominant infection among adults aged 25–39 years.

An international WHO-Africa CDC mission recently assessed the response, noting strong coordination and rapid testing capacity but highlighting challenges such as high test positivity, limited isolation facilities, and suboptimal contact tracing.

Other African Countries

Burundi has reported a significant decrease in cases, now below 50 per week, down from over 200 at the peak. Other countries with active clade Ib community transmission include Rwanda, Kenya, Zambia, Republic of Congo, United Republic of Tanzania, South Sudan, and Malawi.

Molecular Epidemiology and Virus Evolution

The multi-clade presence and varied transmission dynamics illustrate the complex epidemiology of mpox:

• Clade Ia outbreaks have traditionally been linked to zoonotic sources with limited human spread. However, Kinshasa’s urban transmission highlights the virus’s evolving capacity for sustained human transmission, including sexual contact routes.
• Clade Ib shows exclusive human-to-human transmission without documented animal reservoirs, pointing to a viral adaptation and spread within interconnected human networks, including sexual networks. This clade has sparked community transmission clusters in multiple African countries and travel-associated cases globally.
• Clade IIa remains poorly understood but is associated with sporadic zoonotic spillovers in West Africa, with limited human transmission evidence.
• Clade IIb is well-characterized as spreading mainly through sexual contact among MSM globally but occasionally spills over to other groups without sustained spread.

The genomic surveillance efforts, particularly in DRC, are crucial for tracking viral evolution, transmission chains, and informing public health strategies.

Public Health Response and Challenges

Surveillance and Diagnostics

WHO continues to support indicator-based surveillance, data integration, and laboratory diagnostic capacity. Rapid diagnostic tests (RDTs) are under field evaluation in DRC, with PCR assays undergoing performance validation globally. Surveillance data is updated weekly for Africa and monthly at the global level, with continued efforts to improve data completeness and accuracy.

Challenges include limited PCR testing capacity in some settings, especially in DRC, causing underreporting and delays. Syndromic surveillance complements laboratory confirmation but requires careful interpretation.

Case Management and Infection Prevention

Strengthening clinical care capacity remains a priority, ensuring availability of essential medicines and supplies, infection prevention and control (IPC) practices, and water, sanitation, and hygiene (WASH) support.

WHO promotes use of clinical characterization tools and data platforms to understand clinical presentations and improve treatment protocols.

Hand hygiene and IPC are emphasized to reduce transmission in healthcare and community settings, supported by guidance and educational materials.

Vaccination Strategies

Mpox vaccination efforts have scaled up in seven African countries, with over 668,000 doses of the Modified Vaccinia Ankara-Bavarian Nordic (MVA-BN) vaccine administered, predominantly in DRC (87% of doses).

Due to limited vaccine supply, WHO recommends dose-sparing strategies, including single-dose regimens and intradermal fractional dosing, with prioritization of high-risk groups such as healthcare workers, contacts of cases, sex workers, men who have sex with men, and other vulnerable populations.

Each country’s vaccination approach reflects local epidemiology and resource availability. For example:

• DRC: Started with two-dose regimen targeting adults, shifted to single-dose for ages 1+ in high transmission areas. Microplanning is ongoing to optimize vaccine use.
• Uganda: Single-dose vaccination targeting 12+ key populations.
• Rwanda, Nigeria, Sierra Leone, Liberia, Central African Republic: Various stages of vaccination, focusing on high-risk adults and frontline workers.

Global Coordination and Strategic Framework

WHO’s response to the mpox outbreak is guided by the Health Emergency Prevention, Preparedness, Response and Resilience (HEPR) framework, implemented through the Strategic Preparedness and Response Plan (SPRP) for 2024–2027. The plan focuses on five core components, termed the “5Cs”:

1. Emergency Coordination: Continuous coordination through WHO and Africa CDC teams; preparation for upcoming International Health Regulations Emergency Committee meetings.
2. Collaborative Surveillance: Data sharing, laboratory coordination, diagnostic test evaluation, and genomic surveillance.
3. Community Protection: Risk communication, community engagement, stigma reduction, and social-behavioral research.
4. Safe and Scalable Care: Strengthening health systems for case management and IPC.
5. Access to and Delivery of Countermeasures: Ensuring equitable access to vaccines, diagnostics, and therapeutics.

Efforts include technical guidance, operational support, and resource mobilization to strengthen national responses and address gaps identified in outbreak assessments.

Risk Assessment and Outlook

The latest rapid risk assessment conducted by WHO in February 2025 categorizes the global public health risk from mpox as moderate, considering virus transmissibility, spread potential, and response capacities. The risk varies by clade:

• Clade Ib MPXV: High risk, due to rapid human-to-human transmission and international spread mainly through sexual contact.
• Clade Ia MPXV: Moderate risk, with zoonotic spillover and increasing human transmission, especially in DRC.
• Clade IIa MPXV: Moderate risk, with limited human transmission.
• Clade IIb MPXV: Moderate risk, with ongoing outbreaks in MSM populations globally.

The virus is expected to continue evolving and spreading in human populations, with risks influenced by local epidemiology, immune status, and public health interventions.

The mpox multi-country outbreak remains a significant public health challenge in 2025, particularly in Central and East Africa. Persistent transmission of multiple viral clades, evolving epidemiology, and recent surges in countries like Sierra Leone underscore the need for continued vigilance, surveillance, and response adaptation.

Vaccination efforts, diagnostics expansion, and enhanced clinical care are critical pillars of the response, while community engagement and addressing social determinants remain central to breaking transmission chains.

Global coordination through WHO, Africa CDC, and partner agencies continues to evolve, focusing on equitable access to countermeasures and strengthening health systems to mitigate this complex outbreak.

Continued genomic surveillance, operational research, and risk communication will be essential to inform effective strategies and protect vulnerable populations as the outbreak unfolds.