The California Department of Public Health issued a formal health alert on June 16, 2026, warning healthcare providers, laboratories, and local health departments of a significant and accelerating increase in mpox clade I cases in California and the United States — and directly flagging the ongoing World Cup as a factor likely to drive additional imports.
The alert states: "There has been an increase in travel-related introductions of clade I mpox into California and the U.S. in 2026 and clade II mpox cases have increased in California. Increases in clade I community transmission in Western Europe suggest that additional travel-related clade I mpox cases should be expected in California." The full alert is available through the City of Pasadena's Public Health Emergency network, which distributes CDPH clinical bulletins.
The numbers tell the story clearly. Since January 2026 alone, California has reported seven travel-related clade I mpox cases, more than the total of five cases reported across all of 2024 and 2025 combined. Nationally, the CDC has confirmed 25 travel-related clade I mpox cases since November 2024, with more than half occurring since March 2026. The acceleration is visible in the data.
What Clade I Is — and Why It Differs From the 2022 Outbreak
The mpox virus has two main clades — clade I and clade II. The 2022 global outbreak that infected tens of thousands worldwide, including more than 30,000 people in the United States, was caused by clade II, a less severe variant. Clade I, particularly the clade Ib subvariant that has been driving spread in Central Africa, is associated with more severe disease, higher hospitalization rates, and has shown the capacity to spread person-to-person through close contact, including sexual contact, in a manner consistent with sustained community transmission.
As the Los Angeles County Department of Public Health's LAHAN alert network documented, CDPH has separately identified local community spread of clade I mpox within California itself, with three cases in Southern California, including cases in Long Beach and Los Angeles, confirmed without any history of recent international travel, indicating person-to-person local spread. Those cases were identified in late 2025 and required hospital care.
CDPH advises clinicians to "have a heightened index of suspicion for mpox and particularly for clade I mpox in individuals who report recent international travel or sexual or intimate contact with someone who recently traveled internationally, especially to an area where clade I is circulating." Clinicians are directed to report any suspected clade I cases immediately.
| Mpox Clade I U.S. and California Data (Through June 16, 2026) | Count |
| Total U.S. clade I cases (since November 2024) | 25 |
| California clade I cases in 2026 (travel-related) | 7 |
| California clade I cases in all of 2024 and 2025 | 5 |
| U.S. cases occurring since March 2026 | More than 50% of 25 total |
| Locally acquired clade I cases in Southern California | 3 (late 2025) |
| Clade II cases in California (2026 weekly average) | 14.5 per week |
The World Cup Factor — and Who Needs to Act
The CDPH alert's direct mention of the World Cup as a risk amplifier is striking in its specificity. The June 11-July 19 tournament has brought millions of international visitors into 11 U.S. cities, including Los Angeles, Houston, Dallas, San Francisco, and Atlanta, creating dense mixing between visitors from countries where clade Ib is circulating in Europe and Africa. The alert's framing reflects a clinical reality: mass gatherings with international travel, sexual networking, and close physical contact have historically been associated with mpox amplification.
CDPH recommends mpox vaccination with two doses for individuals who may be at risk — including those with multiple sexual partners or who are immunocompromised. The JYNNEOS vaccine (Bavarian Nordic) is expected to provide protection against both clade I and clade II mpox and all known subclades. Two doses are required for full protection.
Mpox symptoms include rash, which often begins on the face and spreads to the rest of the body, including the genitals and hands, along with fever, body aches, chills, swollen lymph nodes, and exhaustion. Clade I disease can produce more painful, extensive lesions that more frequently require hospitalization than clade II. Anyone who develops an unexplained rash after traveling internationally or after close contact with someone who has traveled should contact a healthcare provider promptly, avoid close physical contact until evaluated, and not share towels, clothing, or bedding.
Frequently Asked Questions
What did California's June 16 mpox alert say?
CDPH's June 16, 2026 health alert warned healthcare providers of an accelerating increase in travel-related clade I mpox cases in California and nationally, flagging that clade I community transmission in Western Europe means additional U.S. cases are expected, and citing the World Cup as a factor that increases the likelihood of importation.
How many clade I mpox cases have there been in California and the U.S.?
As of the June 16 CDPH alert, California has reported seven travel-related clade I mpox cases in 2026 alone — surpassing the five cases from all of 2024 and 2025. Nationally, the CDC has confirmed 25 clade I cases since November 2024, with more than half occurring since March 2026.
What is the difference between the mpox clade I and the 2022 clade II outbreak?
Clade I is associated with more severe disease, higher hospitalization rates, and has shown capacity for person-to-person community transmission. The 2022 global outbreak was driven by clade II, which is generally less severe. California has confirmed three locally acquired clade I cases in Southern California without any travel history, indicating domestic spread is already occurring.
Who should get vaccinated against mpox?
CDPH recommends two doses of the JYNNEOS vaccine for individuals who may be at risk, including those with multiple sexual partners, immunocompromised individuals, and healthcare workers who may have contact with mpox patients. The vaccine is expected to protect against both clade I and clade II.
What are the symptoms of clade I mpox?
Clade I mpox typically presents with rash — often starting on the face and spreading to the body, genitals, and extremities — combined with fever, lymph node swelling, muscle aches, and fatigue. Clade I lesions are often more severe and painful than clade II, and clade I is more likely to require hospitalization. Anyone with an unexplained rash after travel or close contact with a traveler should seek medical evaluation immediately.
