The U.S. Centers for Disease Control and Prevention (CDC) has reported a significant shift in the epidemiology of Clade I mpox in the United States. In its September 25 update, the CDC confirmed more than 60 laboratory-confirmed Clade I cases across at least 20 states. Critically, since August, an increasing proportion of these cases have occurred among individuals with no recent international travel or known links to travelers. Cases with presumed domestic transmission have now been reported in more than 10 jurisdictions, leading the CDC to state that this indicates a “likely transition to sustained Clade Ib transmission in the United States.” While the CDC continues to assess the risk to the general U.S. population as low, it expects additional travel-related and domestically acquired cases.
This development matters because it marks a departure from previous U.S. surveillance. As recently as August, the CDC reported that sustained Clade Ib transmission had not been detected in the United States during 2024–2025. The new assessment represents a likely transition toward sustained domestic transmission. The 2022 global mpox outbreak, including the large U.S. outbreak, was caused by Clade IIb. Clade I mpox has historically been associated with more severe disease and higher mortality than Clade II, though recent Clade Ib cases in high-income countries have generally involved relatively mild illness. The significance extends beyond disease severity: the changing geographic footprint and transmission dynamics of mpox in the United States signal a need for heightened vigilance and preparedness.
GeoVax Labs, Inc. (Nasdaq: GOVX), a clinical-stage biotechnology company developing vaccines against infectious diseases and therapies for solid tumor cancers, highlighted the CDC's update. David Dodd, Chairman and CEO of GeoVax, commented, “CDC’s latest assessment represents an important change in the epidemiology of Clade Ib mpox in the United States. While the risk to the general population remains low, presumed domestic transmission across multiple jurisdictions reinforces the importance of continued surveillance, vaccination of appropriate at-risk populations and sustained preparedness.” Dodd continued, “Preparedness should not begin when an infectious-disease threat becomes a crisis. The appropriate time to strengthen vaccine capacity, diversify sources of supply and establish scalable manufacturing infrastructure is before those capabilities are urgently needed.”
GeoVax is advancing GEO-MVA, a Modified Vaccinia Ankara (MVA)-based vaccine being developed for protection against mpox and smallpox. Following formal guidance from the European Medicines Agency (EMA), GeoVax is advancing GEO-MVA through an expedited clinical development pathway, with traditional Phase 1 and Phase 2 trials not required. The program will proceed directly to a pivotal Phase 3 immunobridging study comparing immune responses generated by GEO-MVA with those generated by the licensed MVA-BN comparator. GeoVax expects to initiate the 500-participant pivotal Phase 3 study in the fourth quarter of 2026, with results expected in mid-2027. The company is developing GEO-MVA to expand global access to MVA vaccines and scalable production capabilities, with the potential to provide governments and international public health organizations with an additional source of MVA vaccine. For more information, visit www.geovax.com.
The changing mpox landscape follows other recent public-health preparedness actions, including updated CDC vaccination recommendations for certain U.S. travelers at increased risk and international initiatives to strengthen access to mpox vaccines and outbreak-response capabilities. Globally, Clade I outbreaks have continued in Central and Eastern Africa since late 2023, with subsequent geographic expansion beyond the region, including transmission in parts of Europe and introductions into the United States. Dodd concluded, “Low risk to the general population today and the need for long-term preparedness are not contradictory. CDC’s latest assessment illustrates why preparedness must anticipate changes in infectious-disease transmission rather than react to them after they occur. We believe diversified vaccine supply and scalable MVA manufacturing capacity can become increasingly important as the epidemiology of mpox continues to evolve.”
