Mpox Updates for Clinicians

Content From: Jonathan Mermin, MD, MPH, RADM and Assistant Surgeon General, USPHS, Director, National Center for HIV, Viral Hepatitis, STD, and TB Prevention, Centers for Disease Control and PreventionPublished: December 21, 20234 min read



Cross-posted from: CDC’s National Center for HIV, Viral Hepatitis, STD, and TB Prevention

December 20, 2023

Dear Colleague:

I am writing to you today with a reminder that mpox continues to circulate in the United States. Although case counts are lower than they were last year, severe manifestations, including deaths, continue to occur. Convinced by the benefits of the vaccine, the Advisory Committee on Immunization Practices now recommends persons with potential risk of exposure receive two doses of the JYNNEOS vaccine. Despite this, only one in four of the approximately two million people eligible to receive the vaccine in the United States have received both doses. In addition to the Clade II mpox virus (MPXV) cases that have been reported in the United States since May 2022, the Centers for Disease Control and Prevention (CDC) recently issued an advisory to raise awareness about a concerning increase of cases of Clade I MPXV in the Democratic Republic of Congo (DRC). Clade I is associated with increased transmission and more severe illness.

Mpox in the United States

Although reported cases of Clade II MPXV have significantly declined since the height of the outbreak in 2022, small clusters are still occurring in the United States. Within the past two months, some health departments have reported an increase in cases among men who report having sexual contact with men.1,2 Unfortunately, deaths continue to occur in individuals who are severely immunocompromised, including advanced HIV disease. Vaccination remains an important, but underutilized, tool in stopping the spread of MPXV. Modeling data suggest that if vaccine coverage in the United States does not increase, we may experience large outbreaks in the future.

What you can do:

  • Remain alert for patients presenting with MPXV symptoms and test patients who have a rash illness consistent with MPXV regardless of whether other etiologies are more likely.
  • Continue to recommend the two dose JYNNEOS vaccine to eligible patients.
  • Encourage patients who have only received one dose to get the second dose to have the best protection.
  • Conduct a comprehensive sexual history of your patients, which will help you determine what additional counseling or testing to provide. Additionally, test all sexually active people with suspected MPXV for HIV and other STIs and provide treatment to those with positive test results.

Mpox in the DRC

MPXV has two distinct genetic clades (or subtypes), I and II. CDC issued a Health Advisory to notify clinicians and health departments about the occurrence, geographic spread, and sexually associated human-to-human transmission of Clade I MPXV in the DRC. While Clade I MPXV has not been detected in the United States, clinicians should be aware of the possibility of Clade I MPXV in travelers returning from the DRC. Clade I spreads similarly to Clade II, the MPXV type associated with the 2022-23 global outbreak, but may be more transmissible and cause more severe infections. Vaccines and other medical countermeasures are available and expected to be effective for both Clade I and Clade II MPXV infections.

What you can do:

  • Notify your state health department if you have a patient with mpox-like symptoms and recent travel to the DRC.
  • Submit lesion specimens for clade-specific testing for these patients. Some non-CDC laboratories may also have options available for clade-specific testing. If clade-specific testing is not available in a jurisdiction, specimen submission to CDC is encouraged; specimen submission to CDC can be coordinated through your state or local health department.
  • Test all sexually active people with suspected mpox for HIV and other STIs and provide treatment to those with positive test results. People with advanced HIV, or who are severely immunocompromised, are at increased risk of severe illness and death if they get the mpox virus.

I also encourage you to administer the JYNNEOS vaccine in your clinic, if possible. If the vaccine is not available in your clinic, share the vaccine finder and prevention information with your patients. Please also circulate this letter among your colleagues for broader awareness and action.

Thank you for your continued efforts to stop the spread of MPXV and protect individuals and communities across the nation and abroad.


/Jonathan Mermin/

Jonathan H. Mermin, MD, MPH
Rear Admiral and Assistant Surgeon General, USPHS
National Center for HIV, Viral Hepatitis, STD, and TB Prevention
Centers for Disease Control and Prevention
Stay connected: @DrMerminCDCExit Disclaimer and Connections

  2. Outbreak of Mpox in King County – King County, Washington