Severe Mpox Clade I Detected in U.S.: Ex-CDC Official Assesses Federal Readiness

Alarming Shift: Highly Severe Mpox Clade I Cases Emerge in California

The public health landscape surrounding mpox (formerly monkeypox) has shifted dramatically following the detection of the more virulent Clade I strain in the United States. Recent reports confirm three cases of mpox Clade I in California, a development that has immediately raised concerns among infectious disease experts and federal health officials.

Crucially, all three individuals infected with this strain required hospitalization, underscoring the increased severity associated with Clade I compared to the strain responsible for the global outbreak in 2022. This emergence has prompted a former senior official from the Centers for Disease Control and Prevention (CDC) to issue a candid assessment of the current state of federal resources and preparedness in 2025.

Understanding the Threat: Clade I vs. Clade IIb

The primary concern surrounding these new cases stems from the fundamental difference in virulence between the two main mpox clades. The global outbreak that began in 2022 was overwhelmingly caused by Clade IIb, which, while highly transmissible, has a relatively low fatality rate (typically less than 1%).

Clade I, conversely, is the strain historically found in Central Africa and is known to cause far more severe illness. Historically, the fatality rate associated with Clade I has been reported to be as high as 10%. The fact that all three initial California patients required intensive medical care highlights the immediate danger this strain poses to public health.

Key Differences in Mpox Clades

Treatment Availability

For treatment, the antiviral drug TPOXX (tecovirimat) remains the primary therapeutic option. While TPOXX was widely used during the 2022 outbreak, its use required significant paperwork and regulatory hurdles due to its status as an Investigational New Drug (IND) protocol. The former official stressed that federal agencies must streamline access to TPOXX, especially given the increased likelihood of severe outcomes and hospitalization with Clade I.

Expert Warning: The Need for Heightened Surveillance

The former CDC official highlighted that the most significant vulnerability in the current system is the potential for missed diagnoses, especially as mpox cases have dropped significantly since the 2022 peak. Complacency in the healthcare system could allow Clade I to spread undetected.

Key areas requiring immediate federal attention include:

1. Enhanced Laboratory Capacity: Ensuring state and local labs have the necessary resources and protocols to rapidly differentiate between Clade I and Clade IIb, as this distinction is vital for clinical management and public health response.
2. Targeted Public Health Messaging: Re-engaging high-risk populations with clear, non-stigmatizing information about the new, more severe threat and the availability of the Jynneos vaccine.
3. Clinical Awareness: Educating clinicians, particularly in emergency rooms and primary care settings, to maintain a high index of suspicion for mpox, even if the patient does not fit the typical profile seen during the 2022 surge.

The Operational Challenge

The official noted that the federal government’s response apparatus, managed by agencies like the CDC and the Department of Health and Human Services (HHS), must be ready to transition from a low-level monitoring phase back into a high-alert response phase. This includes activating contracts for testing supplies and ensuring communication channels between federal, state, and local health departments are seamless.

Key Takeaways for the Public

This development signals a critical moment for public health vigilance. The emergence of mpox Clade I in California requires both federal action and public awareness.

• Increased Severity: Clade I is significantly more dangerous than the strain seen in 2022, leading to higher hospitalization rates and a greater risk of severe outcomes.
• Vaccine Protection: The Jynneos vaccine remains effective against Clade I. Individuals in high-risk categories should ensure they are fully vaccinated.
• Treatment Access: The federal government must ensure that TPOXX is readily accessible to clinicians treating Clade I patients to mitigate severe illness.
• Vigilance is Key: Healthcare providers and the public must remain vigilant for symptoms, which include characteristic rashes, fever, and swollen lymph nodes, and seek testing immediately.

Conclusion: A Call for Renewed Focus

The detection of mpox Clade I in the U.S. is not merely a statistical anomaly; it is a clear warning that the threat posed by the virus has evolved. The former CDC official’s assessment underscores that while the U.S. possesses the necessary medical countermeasures—vaccines and treatments—the effectiveness of the response hinges entirely on the operational readiness of federal and state public health systems.

Moving forward, sustained funding for surveillance, rapid deployment of existing resources, and clear, consistent communication will be essential to prevent the more severe Clade I strain from gaining a foothold and causing a public health crisis similar to, or potentially more dangerous than, the 2022 outbreak.