Two Monkeypox Strains Are Spreading Differently Around the World—Here's What That Means for You

Monkeypox isn't spreading the same way everywhere anymore. The virus has evolved into two main types—clade I and clade II—and they're behaving very differently depending on where they're circulating. While clade I cases in the United States remain low, a newer strain called clade Ib is now popping up in Western Europe among people with no recent travel history, suggesting the virus is adapting to spread through intimate contact rather than just travel.

What's the Difference Between These Two Monkeypox Strains?

The two main types of monkeypox—clade I and clade II—can be spread, treated, and prevented in the same ways, but their origins and transmission patterns tell different stories. Clade I emerged from Central and Eastern Africa, where it has caused more than 46,000 cases. Within clade I, there are two subclades: clade Ia and clade Ib, each with distinct characteristics.

Clade Ia, found primarily in Central Africa, spreads through contact with infected animals or through household and healthcare settings. It carries a higher case-fatality rate of about 2.5%, meaning roughly one in 40 infected people may die from the infection. Clade Ib, discovered more recently in eastern Democratic Republic of the Congo, is mostly spread through intimate or sexual contact, followed by household transmission. The good news: clade Ib has a much lower case-fatality rate of less than 0.5%, meaning fewer than one in 200 infected people die.

Clade II, the older strain that caused a global outbreak affecting more than 100,000 cases across 122 countries, continues to circulate at low levels worldwide. A summer 2025 uptick of clade II cases in the United States was linked to outbreaks in West African countries like Sierra Leone and Liberia.

Why Is Clade Ib Appearing in Europe Without Travel Links?

Beginning in fall 2025, several Western European countries started reporting clade Ib monkeypox cases among people with no documented history of international travel. These cases were likely related to sexual exposure, marking a significant shift in how the virus is spreading globally. To date, more than 150 clade Ib cases have been reported in high-income countries since January 2024, and importantly, no deaths have been reported in these regions.

This pattern suggests the virus is establishing itself in new populations through sustained person-to-person transmission rather than relying solely on travelers bringing it from endemic areas. The United States has reported 11 clade I cases since November 2024, mostly in people who traveled to affected areas in Central and Eastern Africa. However, three cases reported in October 2025 had no recent travel history, and genomic data linked them to a case from August 2025, indicating potential local transmission chains.

How to Protect Yourself From Monkeypox

• Get Vaccinated if Traveling: The monkeypox vaccine is recommended for eligible people traveling to areas with active outbreaks, particularly Central and Eastern Africa, or West African countries experiencing clade II spread. Travelers to Liberia should review CDC travel health notices for current vaccine recommendations.
• Practice Safe Intimate Contact: Since clade Ib spreads primarily through intimate or sexual contact, using barrier protection and limiting partners during outbreaks can reduce transmission risk in affected areas.
• Maintain Household Hygiene: Monkeypox spreads through household contact and day-to-day interaction, so regular handwashing, avoiding shared personal items, and proper cleaning of surfaces can help prevent transmission within homes.
• Seek Testing if Symptomatic: If you develop symptoms like rash, fever, or swollen lymph nodes after potential exposure, contact a healthcare provider immediately. Early detection helps prevent further spread.

What's the Current Risk in the United States?

The risk posed by the clade I monkeypox outbreak to most people within the United States remains low, according to the Centers for Disease Control and Prevention (CDC). The country has robust surveillance systems in place, including wastewater testing to detect cases early. The CDC has also increased the number of testing sites and improved specimen transport networks to quickly identify new cases.

However, experts expect additional cases in both Europe and the United States as clade Ib continues to spread through sexual contact networks. The CDC is working closely with state, tribal, local, and territorial public health departments to provide recommendations for clinical management, diagnosis, and prevention. Healthcare providers have been alerted to consider monkeypox as a possible diagnosis in certain patients, ensuring faster identification and treatment.

How Is the Global Response Addressing Monkeypox?

The CDC and international partners are taking a multi-pronged approach to stop monkeypox at its source. In the Democratic Republic of the Congo, the CDC trained 80 field epidemiologists who are now playing a key role in detecting cases, tracing contacts, and increasing community awareness. These trained professionals are also collecting specimens for testing and training healthcare workers in infection prevention and control.

Response efforts across affected regions include several critical components designed to slow transmission and improve detection:

• Laboratory Capacity: Building local lab infrastructure in affected countries to test specimens quickly and accurately, reducing delays in case identification.
• Vaccine Strategy and Planning: Coordinating vaccine distribution with governmental and civil society partners to reach populations most at risk, particularly those with sexual exposure risk.
• Healthcare Worker Training: Strengthening the workforce's ability to recognize monkeypox symptoms, manage cases properly, and prevent transmission in healthcare settings where protective equipment is essential.
• Community Engagement: Working with local communities to increase awareness about monkeypox transmission and prevention, reducing stigma and encouraging people to seek care.
• Surveillance and Monitoring: Collecting and analyzing case data to understand how monkeypox spreads in different settings and populations, informing prevention strategies.

The CDC also works with researchers and partner organizations to increase health equity around monkeypox, ensuring that populations most affected by the virus have access to vaccines and treatment. This includes targeted outreach to communities experiencing outbreaks and those with higher transmission risk.

While monkeypox headlines have faded from news cycles, the virus continues to evolve and spread in new ways. The emergence of clade Ib in Europe without travel links is a reminder that infectious diseases don't follow predictable patterns. By staying informed about transmission routes, getting vaccinated when traveling to affected areas, and maintaining awareness of symptoms, you can protect yourself and your community from this emerging threat.