Thailand's Department of Disease Control has confirmed that the Clade Ib strain of mpox has overtaken all other variants as the dominant circulating form of the virus across the country, accounting for 88 of the 139 cumulative cases recorded this year as of mid-July. The shift marks a significant epidemiological development that public health authorities are responding to with enhanced surveillance, targeted vaccination, and integrated screening protocols in high-risk areas including Bangkok, Chiang Mai, Chon Buri, and Phuket.
Why This Matters
• Clade Ib is the new dominant strain: With 88 confirmed cases out of 139 total this year, Thailand now leads Southeast Asia in reported Clade Ib infections—far ahead of Singapore's two cases and Malaysia's single case.
• Two deaths reported, both among HIV-positive individuals: While neither fatality is directly attributed to Clade Ib, the co-infection highlights vulnerability among immunocompromised populations.
• Targeted vaccine rollout underway: Thailand is deploying limited MVA-BN vaccine supplies to healthcare workers and high-risk groups across four priority provinces.
• Transmission primarily sexual: Most infections trace to close physical and sexual contact, particularly among men who have sex with men (MSM), with cases now appearing across tourist destinations and urban centers.
Strain Dominance Reflects Regional Epidemiological Shift
The Clade Ib variant, first identified in the Democratic Republic of Congo in September 2023, has rapidly expanded its geographic footprint. In Thailand, the strain was initially detected in August 2024 in a travel-related case from Africa. By January 2025, health officials confirmed the country's first Clade Ib cluster, and since late May 2026, infections have surged. The 88 Clade Ib cases now represent the clear majority of Thailand's 2026 mpox burden—a dramatic reversal from earlier in the year when Clade II strains dominated.
Historically, Clade I variants carried case fatality rates between 5% and 10% in African outbreaks, while Clade II strains—responsible for the global 2022-2023 outbreak—generally caused milder disease. Clade Ib, however, exhibits higher transmissibility and is associated with more severe outcomes, particularly in children, pregnant individuals, and people living with HIV/AIDS. Current data from multiple countries suggest that with optimal supportive care, fatality rates for both clades remain relatively low, but delayed diagnosis or inadequate treatment can lead to prolonged illness and complications.
Thailand's two recorded deaths this year occurred among individuals living with HIV, underscoring the heightened risk profile for immunocompromised populations. Neither death has been definitively linked to Clade Ib, though the strain's association with more severe illness in vulnerable groups remains a concern for clinicians and public health planners.
What This Means for Residents
Anyone living in or traveling to Thailand should understand that mpox is now circulating at levels not seen earlier in the year, with the more transmissible Clade Ib variant leading the charge. The average age of patients is 36, and 88.49% of cases are Thai nationals, indicating substantial local transmission rather than imported infections alone.
The primary mode of transmission remains sexual and close physical contact. Public health campaigns are emphasizing the importance of avoiding skin-to-skin contact with anyone displaying suspicious rashes or lesions, refraining from sexual contact with strangers or individuals with visible symptoms, and maintaining rigorous hand hygiene. Personal items such as towels, bedding, and clothing should not be shared.
For those in high-risk groups, particularly MSM and individuals with multiple sexual partners, the Thailand Department of Disease Control is integrating mpox surveillance with existing HIV and sexually transmitted infection (STI) services. This approach leverages established healthcare infrastructure and trusted community networks to improve early detection and contact tracing.
Vaccine Strategy: Limited Supply, Targeted Deployment
Thailand's vaccination program is constrained by limited global supply of the MVA-BN vaccine. As of mid-January 2026, the country received 2,220 vials through ASEAN support, with 2,175 doses distributed to four priority provinces: Bangkok, Chon Buri, Chiang Mai, and Phuket. These doses are allocated for both post-exposure prophylaxis (PEP) for close contacts of confirmed cases and pre-exposure prophylaxis (PrEP) for healthcare workers and individuals exhibiting higher sexual-risk behaviors.
Overall vaccine coverage remains low, which places greater emphasis on non-pharmaceutical interventions: early case detection, mandatory quarantine in hospitals equipped with negative pressure rooms, thorough contact tracing, and public education campaigns. The DDC is also monitoring cases among foreign visitors, given Thailand's status as a major tourist destination and the risks of bidirectional transmission.
Regional and Global Context
Thailand's 88 Clade Ib cases place it significantly ahead of its Southeast Asian neighbors in terms of reported infections. Singapore identified its first two locally transmitted Clade Ib cases in April 2026, both linked to sexual activity and in stable condition. Malaysia reported one Clade Ib case without a travel link as of December 2025, while Cambodia, Indonesia, Vietnam, the Philippines, and Myanmar have reported either no Clade Ib cases or exclusively Clade II infections. Vietnam, for instance, recorded 199 cases with 8 fatalities over two years, but all sequenced strains were Clade IIb—the less severe variant that drove the 2022-2023 global outbreak.
The World Health Organization declared mpox a Public Health Emergency of International Concern in August 2024 due to the rapid spread of Clade Ib in the Democratic Republic of Congo and neighboring African countries. Although the emergency declaration was lifted in September 2025, the WHO continues to advise global emergency preparedness and response activities as both clades circulate worldwide.
The emergence of a recombinant strain combining Clade Ib and Clade IIb, detected in the United Kingdom and India, underscores the virus's evolutionary capacity and the potential for new, more challenging variants. This recombination suggests broader undetected transmission than current surveillance captures and highlights the urgency of extensive genomic sequencing.
Surveillance and Hospital Preparedness
The DDC has intensified surveillance in tourist destinations, crowded venues, and urban centers. Enhanced screening procedures and patient follow-up protocols are now standard practice in high-traffic areas. Confirmed cases are subject to mandatory quarantine and treatment in facilities with negative pressure rooms to prevent airborne transmission, although the primary route of infection remains direct physical contact.
Public health officials stress that early detection and contact tracing are the cornerstones of outbreak control, especially given the limited vaccine supply. The integration of mpox screening into HIV and STI services allows healthcare providers to reach at-risk populations more effectively and reduces stigma associated with seeking care.
Practical Guidance for the Public
Residents and visitors should be aware of the signs and symptoms of mpox: a rash that may begin on the genitals, anus, or face before spreading to other parts of the body, often accompanied by fever, swollen lymph nodes, headache, muscle aches, and fatigue. Atypical presentations—such as isolated genital or perianal lesions—are common with both Clade IIb and Clade Ib.
Anyone experiencing these symptoms should seek medical attention immediately and avoid close contact with others until cleared by a healthcare provider. Healthcare workers and laboratory personnel should follow strict infection control protocols, including the use of personal protective equipment, as healthcare-related exposure has been documented in multiple countries.
The Thailand Ministry of Public Health maintains up-to-date guidance on its website, and the DDC operates a hotline for mpox-related inquiries. Vaccination is available on a case-by-case basis in the four priority provinces, primarily for post-exposure prophylaxis and for individuals identified as high-risk through clinical evaluation.
The Road Ahead
Thailand's experience with Clade Ib reflects a broader global trend: the virus is adapting, spreading through diverse transmission routes, and establishing footholds in new geographic regions. The country's robust surveillance system, hospital preparedness, and integration of mpox screening with HIV/STI services represent a comprehensive response strategy that other nations in the region may look to as a model.
Yet the limited vaccine supply and the virus's high transmissibility mean that behavioral interventions—safer sexual practices, rigorous hand hygiene, and prompt medical attention for suspicious symptoms—remain the most effective tools available to the public. As Thailand continues to monitor the situation closely, the emphasis is on early detection, rapid isolation, and thorough contact tracing to prevent further transmission and protect vulnerable populations.
