A more virulent strain of mpox is expanding its footprint in the United States. As of late May 2026, 23 cases of clade I mpox have been confirmed in the U.S. — a jump from fewer than 15 cases reported earlier in the spring — all diagnosed in individuals who had recently traveled to areas of Central or Eastern Africa with known outbreaks, or who were linked to people with such travel histories. The CDC has explicitly stated that it expects additional cases as summer international travel peaks and the World Cup brings tens of millions of visitors through American airports and host cities.
The distinction between clade I and clade II matters. The 2022 global outbreak that spread to over 100 countries — including the United States, where it caused approximately 32,000 cases — was caused by clade IIb, a version of mpox with a case fatality rate under 0.1 percent in high-income countries. Clade I historically caused mortality rates between 1 and 10 percent in Central African outbreaks, where it has been endemic for decades, though more recent data suggest the current clade Ib strain may cause less severe illness outside endemic settings.
Where the U.S. Cases Are Coming From
The CDC's case tracking data confirms that all U.S. clade I cases have been diagnosed in people with recent travel links to Central or Eastern Africa. The current clade I outbreak in the DRC and surrounding countries — which prompted the WHO to declare a Public Health Emergency of International Concern in August 2024 and which has continued to spread through 2026 — is the source of these importations. Several cases have also been linked to European travel, as the UK, Germany, Belgium, and Ireland have reported clade I cases with sexual transmission among men who have sex with men, representing a more concerning evolution of the outbreak's geographic scope.
New York City, which has been tracking mpox cases continuously since the 2022 outbreak, has recorded 79 total mpox cases in 2026 through May — a figure that includes both clade II and a small number of clade I cases, according to NYC Health data. NYC is also one of 16 U.S. host cities for the 2026 FIFA World Cup, with matches through mid-July.
What the World Cup Adds to the Risk Picture
The convergence of record summer international travel and the World Cup creates a sustained importation pressure on U.S. clade I mpox surveillance that health officials are taking seriously. Travelers arrive from dozens of countries with active or recent clade I transmission, including multiple DRC soccer teams traveling to Houston and Atlanta host cities.
Mpox spreads primarily through close physical contact — skin-to-skin contact, sharing of clothing or bedding with an infected person, and sexual contact. It does not spread through brief casual contact or by breathing the same air as an infected person. The JYNNEOS vaccine (two doses) provides significant protection against both clade I and clade II mpox. The CDC continues to recommend vaccination for people who are at elevated risk, including men who have sex with men with multiple partners, people who have sexual contact with partners of unknown vaccination status, and healthcare workers with potential exposure to orthopoxviruses.
Anyone who develops an unexplained rash, particularly one involving sores on the face, chest, hands, feet, or genitals — especially after travel to Central Africa or close contact with someone who has traveled there — should contact a healthcare provider promptly and disclose their travel and exposure history.
Frequently Asked Questions
Q: How many clade I mpox cases have been confirmed in the U.S. in 2026?
A: As of late May 2026, 23 confirmed cases — all in people with recent travel links to Central/Eastern Africa or connections to such travelers.
Q: Is clade I mpox more dangerous than the strain from the 2022 outbreak?
A: Historically, clade I has been more severe than clade II, which caused the 2022 global outbreak. However, data from the current clade Ib strain suggest it may cause less severe illness than historical clade Ia outbreaks, particularly outside endemic regions.
Q: How does mpox spread?
A: Through close skin-to-skin contact, sexual contact, sharing contaminated bedding or clothing with an infected person, and direct contact with the rash or sores of an infected person. It does not spread through brief casual contact.
Q: Who should get the JYNNEOS mpox vaccine?
A: Men who have sex with men with multiple or anonymous partners; people whose sexual partners have a high exposure risk; and healthcare workers with potential occupational exposure to orthopoxviruses.
