Science1 publisher3 min readPublished
Mpox settles into local spread in the US at more than 2,500 cases a year
Mpox caused 2,800 US cases in 2024 and more than 2,500 in 2025, few of them linked to travel, according to a CDC co-authored report. Ending that home-grown spread will take a sustained public health push of the kind that has since dwindled.
The Scientist · Science desk
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What happened
- Nearly all viral samples analyzed in the same report descend from the strain that set off the 2022 outbreak.
- US mpox mainly affects men who have sex with men, spreading through close contact with sex a major route, and vaccine advice targets this group and their partners.
- Two doses of the JYNNEOS vaccine are 66% to 90% effective together, and Live Science reports that too few at-risk people have likely received both.
- Joel Wertheim of UC San Diego said researchers do not quite know how the virus persists at such low numbers across the whole country.
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Why it matters
- decision Health departments now have to fund mpox vaccine and testing access as a recurring cost for the affected network, because the virus has held above 2,500 cases a year for two years.
- constraint With only a small fraction of cases tied to travel, screening travelers and imported animals can reach little of the transmission now under way.
- exposure People in the affected network who have had one dose or none sit outside the 66% to 90% protection that applies to the full two-dose course.
- constraint Until researchers explain how mpox persists at low numbers nationwide, programs cannot aim at the specific links in the network that keep transmission going.
Case counts alone cannot separate a virus that keeps arriving from one that never left. Before 2022, US mpox turned up sporadically, carried by travelers returning from African countries where the disease is endemic and by imported infected animals [2]. A few thousand cases a year could in principle be that same pattern at a larger scale [3]. The August report has two lines of evidence against it. Travel history tied only a small fraction of cases to trips abroad [3], and the viral lineages lead back to the 2022 outbreak [4]. Live Science summed up the finding: "In short, once the virus arrived, it never went away." [5]
The count is nearly flat. A fall from 2,800 to a little over 2,500 is a drop of less than 11% [18], and the two years together come to more than 5,300 cases [19]. The article does not say how many samples were sequenced, so the share behind "nearly all" is unknown [4].
Ryan Standford, an epidemiologist in the CDC's Poxvirus and Rabies Branch and a co-author of the report, was careful with the label. "There's no set threshold for what constitutes endemicity of monkeypox virus (MPXV) in the United States," he told Live Science. "But each year provides further evidence of this transition." [6]
Who gets infected follows from where the outbreak started. According to Live Science, men who have sex with men are not more prone to infection than anyone else. The virus began spreading in one sexual network and has stayed there [14]. Joel Wertheim, a professor of medicine at the University of California, San Diego, said: "The mpox virus rediscovered the same transmission network that HIV had explored decades earlier." [15] A 2025 paper by Wertheim and colleagues found that the 2022 outbreak in New York City formed "densely connected" clusters, which thinned out as people gained immunity through infection and vaccination [16]. "From an evolutionary, ecological perspective, it's not hugely successful," Wertheim said. "It's sort of barely hanging on as an STI." [17]
Demetre Daskalakis coordinated the national mpox response under the previous administration and is now chief medical officer of Callen-Lorde, an LGBTQ+ community health center in New York City [12]. "We have vaccines, testing, and a much stronger understanding of the disease than we did in 2022," he told Live Science [9]. "Our focus now should be making sure those tools remain accessible, especially for communities that continue to face ongoing risk," he said [10]. He added: "People at increased risk should know that mpox has not disappeared." [11]
In my view, two similar years of home-grown cases are enough to justify running mpox as a standing program for the affected network [3][4]. That means keeping vaccines and testing accessible, as Daskalakis argues, and continuing to sequence samples to check that the 2022 lineage still accounts for nearly all of them [10][4]. Targeting will stay imprecise until someone answers Wertheim's question about how the virus persists at such low numbers [7].
What to watch
- US case counts for 2026: a figure that holds near 2,500 would add to the endemic evidence Standford describes, while a sharp fall would weaken it.
- Two-dose JYNNEOS coverage figures for men who have sex with men and their partners, which would show whether the vaccination gap is closing.
- Any sequenced US case from a lineage other than the 2022 strain, which would mean fresh importations are running alongside local spread.