The detection of clade 1b in the Americas marks a shift in the epidemiological landscape of the disease, which is predominantly associated with clade 2 in the region. Clade 2 was the primary driver of the global mpox outbreak in 2022 and 2023, a wave that affected 145 countries and territories and resulted in a total of 179,612 confirmed cases worldwide. While clade 2 cases in the Americas have largely occurred among men who have sex with men, the introduction of clade 1b expands the potential risk profile, as this strain has demonstrated increased transmissibility in the DRC.
Regional data from the Pan American Health Organization (PAHO) and the World Health Organization (WHO) indicates that the Region of the Americas continues to contribute the largest proportion of global mpox cases, accounting for 41% of the total since 2022. This is followed by the African Region (36.2%) and the European Region (17.8%). In the Americas, a cumulative total of 73,641 confirmed cases and 160 deaths have been reported across 31 countries and territories between 2022 and early 2026. However, the immediate situation in 2026 appears stable, with 172 cases reported across eight countries—Argentina, Bolivia, Brazil, Canada, Chile, Colombia, Mexico, and the United States—and no deaths recorded in the region to date.
The spread of clade 1b to the Americas has been gradual. To date, four countries in the region have reported cases of this specific clade: the United States (9 cases), Canada (2 cases), Brazil (2 cases, including the recent São Paulo case and one prior instance), and Mexico (1 case). The most recent surveillance data highlights two imported clade 1b cases confirmed in the last three months, one in Mexico and one in Brazil. In both instances, the individuals were travelers with a history of exposure prior to entering their respective countries and had departed before their test results were confirmed. This pattern suggests that international travel remains a primary vector for the introduction of new viral lineages into the Americas.
Global surveillance efforts, including genomic and virologic tracking, are essential for distinguishing between clades and monitoring infection dynamics. The recent identification in Brazil underscores the need for continued vigilance among healthcare providers and public health authorities. While the current number of clade 1b cases in the Americas remains low compared to the thousands of cases in the DRC, the potential for further spread warrants close monitoring of contact tracing and vaccination strategies.
Concurrently, efforts to develop new preventive tools are underway. Tonix Pharmaceuticals announced that it has received a grant from the US Department of Defense’s Medical CBRN Defense Consortium to support the development of TNX-801, a recombinant live horsepox virus vaccine. The company stated that TNX-801 is designed to offer durable, long-term protection against mpox and smallpox with a single-dose regimen and favorable shipping and storage requirements. Tonix reported that the vaccine has performed well in animal challenges involving mpox clade 1 infections, though it remains in the development phase and is not yet approved for human use.
In related public health developments, the CDC issued a Health Alert Network advisory on March 7, urging healthcare professionals to ensure patients are up to date on measles vaccines, particularly those planning international travel. This follows the confirmation of a measles case in a Howard County, Maryland resident who traveled internationally. Health officials have identified two potential exposure sites: Terminal A at Washington Dulles International Airport on March 5 and the Johns Hopkins Howard County Medical Center Pediatric Emergency Department on March 7. The CDC has confirmed 222 US measles cases so far this year, highlighting the ongoing risk of vaccine-preventable diseases in the context of increased global travel.
The co-circulation of multiple infectious diseases, including mpox and measles, underscores the complexity of current global health surveillance. While mpox clade 2 remains the dominant strain in the Americas, the emergence of clade 1b requires updated clinical awareness and targeted prevention measures. Public health authorities continue to advise individuals with symptoms consistent with mpox to seek medical attention promptly, while emphasizing the importance of vaccination for measles and other preventable illnesses among travelers.
