Notes from the Field: Clade II Mpox Surveillance Update — United States, October 2023–April 2024

Investigation and Outcomes

During October 1, 2023–April 30, 2024, a total of 1,802 probable and confirmed^† mpox cases were reported to CDC by 42 states, the District of Columbia, and Puerto Rico. Whereas local mpox case counts have fluctuated, national counts have remained steady, with an average of 59 cases per week. Cases continue to occur primarily among cisgender men (1,054 [94%] of 1,121 who reported data on gender identity) and those who identified as gay or bisexual (326 [90%] of 361 who reported sexual orientation data). Most cases (62%) occurred among persons aged 25–40 years, with a median age of 34 years (range = 0–76 years); six (0.4%) cases occurred among persons aged <18 years. Race and ethnicity were reported for 1,651 (98%) cases; among these persons, 526 (34%) identified as Hispanic or Latino (Hispanic), 535 (32%) as White, 410 (25%) as Black or African American (Black), 54 (3%) as Asian, 31 (2%) as multiracial, and 59 (4%) as another race, including American Indian or Alaska Native and Native Hawaiian or Pacific Islander.^§ Among 593 persons with mpox who reported HIV status, 282 (48%) were HIV-positive. Among 1,429 patients with mpox and with hospitalization data reported, 145 (10%) were hospitalized during their illness; among these, 72 reported HIV status, 49 (68%) of whom were HIV-positive. Since October 2023, five patients with mpox have died. Among 684 (38%) persons with mpox who reported vaccination status, 458 (67%) persons reported no vaccination against mpox, and 226 (33%) had received at least 1 dose of vaccine against mpox or smallpox. Of those receiving at least 1 dose, only two (1%) were hospitalized during their illness.

Preliminary Conclusions and Actions

MPXV transmission continues at low levels in the United States. CDC continues to perform genomic sequencing and MPXV clade–specific testing to identify MPXV mutations that affect medical countermeasure effectiveness (i.e., resistance to the antiviral tecovirimat) and to aid in clade I surveillance. To date, no clade I mpox cases have been detected in the United States.

The current average of 59 reported cases per week represents a fifty-five-fold reduction, compared with the peak of 3,274 cases reported during the week beginning July 31, 2022 (the peak outbreak week); levels have remained stable since October 2023. Compared with cases reported during May 10, 2022–September 30, 2023, the proportion of cases among Black persons declined by 7 percentage points (from 32% to 25%) and increased among Hispanic persons by 3 percentage points (from 31% to 34%) since October 2023.^¶ Hospitalizations during this period have increased slightly (10% of cases during October 1, 2023–April 30, 2024, compared with 8% during May 10, 2022–September 30, 2023). Mpox-related deaths in the United States remain rare (0.3% of cases since October 2023). More than two thirds (67%) of new mpox cases occur among persons not previously vaccinated. Since the start of the outbreak, 39% of persons at risk for mpox exposure have received at least 1 dose of vaccine, and 25% have received 2 doses (3). Thus, the majority of persons at risk for mpox exposure remain unvaccinated. CDC recommends that persons at risk for mpox exposure, who have not previously recovered from mpox, receive 2 doses of JYNNEOS vaccine and complete the 2-dose vaccination series, irrespective of time since initial dose or route of vaccination.**^,††