Four years after the outbreak that put mpox on front pages worldwide, federal disease detectives have reached a conclusion that changes how the virus should be understood in the United States. It is not returning. It never left, and the pattern now looks more permanent.
A CDC report published Thursday in Morbidity and Mortality Weekly Report analyzed 5,322 mpox cases reported nationally during 2024 and 2025. Its central finding is stated plainly: persistent transmission of clade IIb monkeypox virus, with wide geographic spread over the last three years, "suggests a transition toward endemic circulation."
That word carries practical weight. Endemic means a virus has settled into a continuous background presence rather than arriving in waves that end. For people at highest risk, it changes vaccination from something done in an emergency to routine preventive care.
Two Years of Numbers That Barely Moved
The case counts show stability rather than decline. There were 2,803 cases in 2024 and 2,519 in 2025, with incidence rates of 140 and 126 per 100,000 among the population CDC estimates to be at risk.
Geographic reach narrowed slightly. Cases were reported from 364 U.S. counties and municipalities in 2024, or 11.3 percent, and from 326 in 2025, or 10.1 percent.
The demographic profile held steady across both years. Most patients were male, 96.5 percent in 2024 and 97.8 percent in 2025, with median ages of 35 and 36, respectively. Among male patients, 79 percent reported their sexual orientation as gay or bisexual. Hispanic or Latino patients accounted for 36.3 percent of cases and Black patients for 22.8 percent, both disproportionate relative to their representation in the affected population, which points to differences in access to vaccination and care rather than to differences in behavior.
Deaths were rare. Five occurred in 2024, with a case fatality rate of 0.18 percent, two in unvaccinated patients and three in patients whose vaccination status was unknown. One death occurred in 2025, at a rate of 0.04 percent, in an unvaccinated patient.
The Fall Doubling That Faded by December
One trend in the data deserves attention precisely because it did not become a wave.
Reported cases roughly doubled between September and October, from 423 in 2024 to 873 during the same months in 2025. Then they fell back to 448 during November and December 2025. Overall, 2025 totals still finished below those of 2024.
A doubling that reverses within two months is the kind of signal that surveillance exists to catch and that a headline can easily distort. It did not produce sustained growth, and the report does not describe it as a new outbreak. It shows that transmission is accelerating, which the CDC cites as one reason more work is needed to prevent the spread, rather than treating the 2022 emergency as finished business.
Vaccination Status and a Nearly Tenfold Hospitalization Gap
The most actionable number in the report concerns who ends up in a hospital.
Among 860 patients with complete data, the odds of hospitalization were 9.73 times as high for unvaccinated patients as for those who had completed the two-dose JYNNEOS series, controlling for age group and HIV status. The confidence interval is wide, ranging from 2.93 to 60.65, reflecting the small number of hospitalized vaccinated patients rather than uncertainty about the direction of the effect.
Among patients whose vaccination status was known, unvaccinated people accounted for 76.1 percent of cases, up from 74.3 percent in 2024 to 78.4 percent in 2025. Overall, 9.5 percent of patients with known status were hospitalized, compared with 2 percent among vaccinated patients. Partially vaccinated patients accounted for 9.6 percent of cases, and the CDC excluded them from the model because no hospitalizations were observed in that group, which left the estimate unstable.
Living with HIV also raised the odds of hospitalization by a factor of 2.37 after controlling for age and vaccination, with a confidence interval of 1.52 to 3.74. Roughly 42 percent of patients with known HIV status were living with HIV.
CDC's recommendation is unchanged and specific: people at risk for exposure should complete the two-dose JYNNEOS series, including travelers to countries with ongoing clade I or clade II transmission. That guidance follows ACIP recommendations for people at risk. Reported effectiveness in a systematic review of real-world vaccine performance runs 35 to 86 percent for one dose and 66 to 90 percent for two, and coverage estimates in this report show no evidence that vaccine-conferred immunity is waning.
Mpox presents as a vesicular rash illness. Among patients with lesion data, the most commonly reported locations were the genitals, at 57.4 percent, followed by the arms, head or neck, trunk, face, and hands. Anyone with an unexplained rash, particularly after close or sexual contact, should contact a clinician and mention mpox by name so the right test is ordered.
Genomic Tracing and What Arrives from Abroad
Sequencing gives the report its second layer. About 97.5 percent of U.S. sequences descended from the 2022 outbreak lineage, confirming that domestic transmission is a continuation rather than repeated reintroduction.
Investigators identified 21 separate importation events. Eleven clade Ib cases were reported over the two years, one in 2024 and ten in 2025, and three of those patients were hospitalized and recovered without antiviral treatment. No clade Ib deaths were reported. A three-case cluster in October 2025 was linked to a travel-associated introduction and did not spread further, a sequence described in a detection of community transmission in the United States. No sustained clade Ib transmission was detected domestically, though sustained transmission continues in several European countries, where about 89 percent of cases occur among men who have sex with men.
Twelve cases of clade IIb lineage A.2.2 appeared across eight states, ten of them in travelers returning from countries experiencing outbreaks of the lineage driving West African outbreaks. That lineage has affected males and females in similar proportions abroad, with evidence of heterosexual transmission. The two remaining U.S. patients had no available travel history, and their sequences carried more mutations than expected for locally circulating virus, which led the CDC to conclude these were importations rather than community spread.
Substantial limitations apply. Passive surveillance misses mild infections for which people do not seek care. Vaccination status was missing for 62 percent of cases, HIV status for 68 percent, sexual orientation for 70 percent, and lesion location for 75 percent, so the percentages describe reported cases with available data rather than a defined population.
MedicalDaily previously reported on clade I importations during heightened summer travel. CDC says further clade Ib importations were observed in 2026 and are expected. Treatment, infection control, and vaccination recommendations remain the same regardless of clade.
Key Questions Answered
What is the main finding? CDC reports 5,322 mpox cases in 2024 and 2025 and says persistent clade IIb transmission suggests a transition toward endemic circulation.
Does endemic mean it is getting worse? No. It means continuous low-level presence rather than waves that end. Case counts were stable and slightly lower in 2025 than in 2024.
Who is most affected? Mostly men, median age 35 to 36, with 79 percent of male patients reporting a gay or bisexual orientation. Hispanic and Black patients were disproportionately represented.
How much does vaccination matter? Unvaccinated patients had 9.73 times the odds of hospitalization compared with those who completed two JYNNEOS doses.
Is the vaccine losing effectiveness? The report found no evidence of waning vaccine-conferred immunity.
What about the more severe clade I? Eleven clade Ib cases were reported over two years, all linked to travel or a single contained cluster. No sustained domestic transmission was detected.
What symptoms should prompt a call? An unexplained rash, most often on the genitals but also on the arms, head, neck, trunk, face or hands. Mention mpox so the right test is ordered.
