A worrying development, but experts say the public risk remains low

Health officials in California have confirmed the first U.S. case of a severe mpox strain (Clade I) in a patient with no recent travel history. The case marks a significant shift in how the virus may be spreading, suggesting possible undetected local transmission of a strain previously limited to parts of Africa.

The patient, a Long Beach resident, was hospitalized before being discharged to recover in isolation at home. Officials have not released identifying details such as age or gender, citing privacy concerns.

While this is the seventh case of the more severe mpox strain in the U.S. this year, it is the first confirmed instance without travel to Africa, where Clade I infections are endemic.

What is mpox and how severe is the new strain?

Mpox, formerly known as monkeypox, is a viral infection caused by the monkeypox virus, a close relative of the smallpox virus. The infection typically leads to fever, swollen lymph nodes, and a characteristic rash that can appear on the face, hands, chest, mouth, or genitals.

Most patients recover in two to four weeks, but severe cases can occur, especially in individuals with weakened immune systems.

Scientists categorize mpox into two genetic lineages, or clades:

• Clade I: Historically linked with higher rates of severe illness and death. Endemic in Central and West Africa.
• Clade II: Responsible for the 2022 global outbreak, which led to more than 100,000 cases across 122 countries, including over 30,000 in the U.S.

The newly identified case in California involves Clade I, the more virulent type that has been spreading across parts of Africa since 2023.

“This underscores the importance of continued surveillance, early response, and vaccination,” Long Beach Mayor Rex Richardson said in a statement, emphasizing that the city is “taking the situation very seriously.”

Why this case matters: signs of possible local transmission

Until now, all U.S. cases of Clade I mpox have been directly linked to travelers returning from outbreak regions in Central or East Africa. The California case, however, breaks that pattern.

Health officials are investigating how the patient contracted the virus, exploring potential domestic transmission pathways, a development that could reshape current containment strategies.

According to the Centers for Disease Control and Prevention (CDC), there is no immediate evidence of widespread community transmission, but contact tracing and genomic sequencing are underway to determine whether this strain is circulating locally.

Public risk remains low, experts say

Despite the concerning implications, the CDC has reiterated that the risk to the general public remains low. Transmission typically requires close, prolonged contact, including skin-to-skin exposure, respiratory droplets, or contaminated materials such as bedding or clothing.

Still, experts warn that the appearance of a more severe strain without travel links is a reminder that viruses evolve and adapt.

“This case doesn’t mean we’re facing a new outbreak, but it’s a wake-up call for vigilance,” said Dr. Alok Patel, an ABC News medical contributor.

How the U.S. is responding to mpox

Following the confirmation, CDC officials issued an alert to healthcare providers nationwide, urging them to test patients with mpox-like symptoms and report suspected cases promptly.

California’s public health department is coordinating with local hospitals and labs to ensure rapid detection and vaccination among high-risk groups.

In November 2024, California recorded the first domestic case of the severe Clade I strain, but that patient had recently traveled from Africa and experienced only mild illness. The new case, without such travel, represents a different epidemiological challenge.

The role of vaccines and prevention

The JYNNEOS vaccine, approved by the U.S. Food and Drug Administration (FDA) for preventing smallpox and mpox, remains the primary tool for protection. It’s administered in two doses, typically four weeks apart.

The CDC recommends vaccination for:

• People with multiple sexual partners, particularly gay, bisexual, and other men who have sex with men (MSM).
• Those who had close or intimate contact with someone diagnosed with mpox.
• Individuals working in laboratory or clinical settings who may be exposed to orthopoxviruses.

Global context: outbreaks in Africa raise red flags

The World Health Organization (WHO) recently declared mpox a public health emergency, following sustained person-to-person transmission of the severe strain in several African nations.

Experts suspect that increased global travel and animal-to-human spillover events could be contributing to its gradual spread beyond endemic regions.

For years, Clade I mpox remained confined to limited geographies. But with the California case showing potential local transmission, health agencies worldwide may need to reassess surveillance systems and vaccine deployment strategies.

What’s next?

For now, the U.S. CDC and California health officials stress that the situation is under control. The ongoing investigation will reveal whether the Long Beach case was an isolated infection or part of a larger, undetected chain of transmission.

Public health experts urge continued vigilance, not panic.
Vaccination, early testing, and awareness of symptoms remain the best tools to prevent outbreaks from escalating.

“Viruses don’t respect borders,” one CDC official noted. “Every case is a reminder of why global surveillance matters.”

TL;DR

• California confirmed the first U.S. case of the severe mpox strain (Clade I) with no travel history.
• Officials are investigating possible local transmission, though public risk remains low.
• The JYNNEOS vaccine continues to provide protection, especially for high-risk populations.
• CDC and WHO emphasize surveillance and preparedness as the virus evolves globally.