Mpox has not gone away in the United States. A new CDC report published Aug. 20 in the Morbidity and Mortality Weekly Report (MMWR) finds that clade IIb monkeypox virus, the strain responsible for the 2022 global outbreak, has continued circulating at low but persistent levels through 2024 and 2025, with a notable surge last fall that briefly doubled case counts compared to the year before.
CDC investigators analyzed national surveillance data covering January 2024 through December 2025, drawing from case reports submitted by state and local health departments along with genomic sequencing data used to track how the virus is evolving and spreading. The United States recorded 2,803 mpox cases in 2024 and 2,519 in 2025, a broadly similar annual total that masks a sharp seasonal spike: reported cases roughly doubled from 423 during September and October 2024 to 873 during the same two months in 2025, before falling back to background levels by the end of December.
The demographic pattern of who gets infected has remained stable since the virus first emerged as a major outbreak in 2022. Cases continue to disproportionately affect men, who made up 97 percent of infections with known sex, and specifically men who have sex with men, who accounted for roughly two-thirds of male patients with known sexual orientation. Black and Hispanic patients continued to be disproportionately affected relative to their share of the at-risk population. The median patient age held steady at around 35, essentially unchanged from prior years.
Vaccination status played a significant role in clinical outcomes. Unvaccinated patients had 9.7 times the odds of hospitalization compared with those who completed the two-dose JYNNEOS series, after accounting for age and HIV status, a gap consistent with the vaccine’s estimated effectiveness of 66 to 90 percent after two doses. 76 percent of patients with known status had received no doses, and only 14 percent had completed the full series. People living with HIV also faced more than double the hospitalization risk of HIV-negative patients, regardless of vaccination status.
Genomic sequencing found that roughly 97.5 percent of U.S. mpox samples from this period trace back to the same lineage that drove the original 2022 outbreak, indicating the ongoing spread reflects ordinary transmission of an already established strain rather than a new variant taking hold. Researchers did identify 21 likely importation events during the two-year period, including 10 cases of clade Ib, a more severe strain first identified in the Democratic Republic of Congo in late 2023 that has since spread across roughly 40 countries. Notably, three of those U.S. clade Ib cases in October 2025 formed a small domestic cluster traced back to a travel-related introduction, marking a documented instance of the more dangerous strain spreading locally on U.S. soil, though investigators found no evidence it continued spreading beyond that limited cluster. Separately, a dozen cases involving a lineage associated with outbreaks in West Africa, where the virus has shown some evidence of heterosexual transmission, all appeared to be tied to travel rather than local spread within the United States.
Rather than treating mpox as a contained emergency that will eventually disappear, a sustained investment is needed in routine surveillance to catch genomic changes early, continued outreach to populations at highest risk, and a renewed push toward closing the vaccination gap that current data show is directly costing lives and driving hospitalizations.
Sources and further reading:
Sandford R, Tuttle A, Aeschleman L, et al. Monkeypox Virus Surveillance, United States, 2024-2025. MMWR, August 20, 2026.
This article was researched and sourced by Global Biodefense editors and reported with Claude AI assistance for drafting and editing.