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October 11, 2023

Outbreak of Mpox in King County

Actions requested

  • Be aware of a recent increase in mpox cases in King County, including among previously vaccinated individuals. In 2023, constant, low numbers of mpox cases continue to be reported in the United States.
  • Continue to recommend vaccination with a complete 2-dose series of JYNNEOS for people at greater risk for mpox infection.
    • Vaccination against mpox remains an important risk-reduction measure.
    • People who previously received only one JYNNEOS vaccine dose should receive a second dose as soon as possible.
    • People who develop mpox after completing a two-dose JYNNEOS vaccine series may experience less severe symptoms than those who have not completed the vaccine series.
    • Avoid conducting extensive risk assessment in people who request vaccination to avoid stigma and other barriers experienced by those who could benefit from vaccine
    • Mpox vaccine may also be given as post-exposure prophylaxis (PEP) to people who are not already fully vaccinated and who have not already had mpox who present with known or presumed exposure to mpox virus. As PEP, vaccine should be given as soon as possible, ideally within 4 days of exposure but administration 4–14 days after exposure may still provide some protection against mpox
    • Additional vaccine administration considerations for specific populations are available on the CDC website
  • Refamiliarize yourself with mpox symptoms, specimen collection, laboratory procedures, and treatment options
    • Consider mpox when determining the cause of a diffuse or localized rash, including patients who were previously infected with mpox or vaccinated against mpox
      • Details noted in patient history, including sexual history may identify possible mpox exposures or epidemiological risk factors
      • Perform a complete physical examination, including a thorough skin and mucosal (e.g., oral, genital, anal) examination which may reveal lesions of which the patient was unaware
      • Mpox may present with milder symptoms in those who were previously vaccinated. Lesions can be few and isolated, pain or discomfort in the throat or rectum can occur with or without classic lesions, and fevers can be absent.
    • Patients benefit from individually tailored supportive care and pain management strategies
    • Continue to consider tecovirimat (also known as TPOXX or ST-246) as first-line therapy for  patients with especially among those with severe complications, severe disease or who are at high risk for severe disease.
    • Encourage patient enrollment both in person and remotely into the STOMP STUDY for recently diagnosed and symptomatic mpox patients. This study evaluates effectiveness and safety of oral tecovirimat, through the UW Positive Research at Harborview Medical Center.
Report all cases of mpox immediately to Public Health at 206-296-4774.


Reports of mpox cases continue in the United States, reflecting ongoing community transmission nationally and internationally. Between January–August, 2023, 30 mpox cases were reported in King County, averaging four new cases each month. The majority of cases did not report travel prior to symptom onset, suggesting local transmission. Since the beginning of September 2023, there have been 11 new cases, including a cluster of three cases reporting attending sex parties during their exposure period. Notably, six of the 11 cases had been vaccinated with a 2-dose series of JYNNEOS; most had been vaccinated approximately one year prior while one case received their dose 2–3 months prior to infection. None were hospitalized. Recent cases have been predominantly among men, ages 18–49 years, particularly among men who have sex with men. Local epidemiology data is updated monthly on the King County mpox online dashboard.

In the 2022 global outbreak of mpox, cases spread rapidly across much of the world through person-to-person contact, disproportionately affecting gay and bisexual men, other men who have sex with men (MSM), and transgender people. However, anyone who has close, personal, skin-to-skin contact with an infected person is at risk of developing mpox. The risk of spread is considered low through touching contaminated objects, fabrics, and surfaces, even without disinfection. This includes items like clothing, bedding, towels, fetish gear, or sex toys. Most patients with mpox have mild disease, although some, particularly those with advanced or untreated HIV infection, may experience more severe outcomes.