A More Dangerous Mpox is Circling: Why California Cases Signal a New Phase of the Virus
Three hospitalizations in California – and none of the patients had recently traveled outside the country. This isn’t a repeat of the 2022 mpox outbreak. Public health officials are now tracking a more virulent strain, clade I mpox, that’s already caused significant illness and death in Central and Eastern Africa. The emergence of locally transmitted cases raises critical questions about how prepared we are for a potentially more serious wave of infection, and what this means for vulnerable populations.
Understanding the Two Faces of Mpox: Clade I vs. Clade II
Mpox, a virus related to smallpox, isn’t a single entity. Researchers have identified two primary clades: I and II. The 2022 global outbreak was driven by clade II, which, while causing significant disruption, generally resulted in milder infections with a fatality rate below 1%. Transmission was largely linked to close physical and sexual contact among men who have sex with men (MSM). However, clade I mpox is a different beast altogether.
Clade I carries a significantly higher fatality rate – around 10% – and has historically been concentrated in the Democratic Republic of Congo (DRC). For years, transmission occurred primarily through direct contact with infected animals, particularly during hunting and butchering. But the situation is evolving. A recent outbreak in the DRC in 2023 demonstrates person-to-person spread, and alarmingly, in some regions, transmission is occurring within families through everyday household activities and in healthcare settings with inadequate protective equipment. This has led to a surge in cases among children under 15.
From Africa to the US: A Shift in Transmission Dynamics
Over 40,000 cases of clade I mpox have been reported in Central and Eastern Africa. Prior to the recent California cases, only six instances of clade I mpox had been identified in the United States, all linked to recent travel to Africa. The fact that the three new cases in California – in Long Beach and Los Angeles County – have no travel history is a stark warning sign. It suggests the virus is now circulating locally, and public health officials are scrambling to pinpoint the source of transmission.
This shift in transmission is particularly concerning because clade I is also demonstrating a new route of spread: sexual transmission, increasingly observed in heterosexual encounters, sex workers, and transient populations like truck drivers. This represents a significant departure from the predominantly MSM-focused transmission patterns seen with clade II.
Why is Clade I More Dangerous? And What Does it Mean for the US?
The higher fatality rate of clade I is a primary concern. However, access to advanced healthcare in the United States could potentially mitigate the severity of infections compared to regions in Africa where healthcare resources are limited. Still, the potential for more severe illness necessitates heightened vigilance.
Experts are closely monitoring the situation, focusing on identifying potential transmission sources and assessing the potential impact on the US population. The CDC is urging healthcare providers to be alert for mpox symptoms and to consider clade I in their differential diagnoses.
Prevention and Vaccination: What You Need to Know
While the overall risk of mpox remains low in the US, proactive measures are crucial. The JYNNEOS vaccine, recommended by the CDC, offers protection against both clades. Current recommendations prioritize vaccination for:
- Gay, bisexual, transgender, or other men who have sex with men who have had (in the last six months) or expect to have:
- One or more sexually transmitted infections
- More than one sexual partner
- Anonymous sexual or intimate contact
- Sex at a commercial sex venue
- Sex in association with a large public event in a geographic area where mpox transmission is occurring
Beyond vaccination, the CDC emphasizes safer sex practices, reminding individuals that the virus spreads through close face-to-face contact, contact with blisters, and contaminated fabrics. The lessons learned during the 2022 outbreak – reduced anonymous sex, minimized skin-to-skin contact, and diligent cleaning of bedding – remain relevant and effective.
Looking Ahead: A Need for Vigilance and Adaptive Strategies
The emergence of locally transmitted clade I mpox in California isn’t simply a recurrence of the 2022 outbreak; it’s a signal of a potentially more dangerous phase of the virus. The changing transmission dynamics, including the rise in sexual transmission outside of the MSM community, demand a broadened public health response. Continued genomic surveillance, rapid case identification, and targeted vaccination efforts will be essential to contain the spread and protect vulnerable populations. The situation underscores the importance of global health security and the need for ongoing investment in research and preparedness.
What steps do you think are most critical to prevent further spread of clade I mpox? Share your thoughts in the comments below!
