At least two genetically distinct monkeypox variants are circulating in the U.S., according to new sequencing data from the Centers for Disease Control and Prevention.

Although the CDC hasn’t sequenced all 22 confirmed U.S. cases yet, two of them were found to be genetically similar to a 2021 infection in a Texas man who traveled to Nigeria. Both are in people who recently traveled to Africa — a woman from Virginia and man from Florida.

The rest of the sequenced U.S. cases resemble the genetic codes of the cases in Europe, and a 2021 infection in a Maryland resident who traveled to Nigeria.

“While they’re similar to each other, their genetic analysis shows that they’re not linked to each other,” Jennifer McQuiston, deputy director of the CDC’s High Consequence Pathogens and Pathology division, said of the two variants at a Friday press briefing.

McQuiston and other disease experts said this new information suggests the U.S. cases stem from two outbreaks instead of one, complicating our understanding of their origins.

“It’s likely that within the last couple of years, there have been at least two different instances where monkeypox virus spilled over to people in Nigeria from the animal that maintains it and that that virus likely began to spread through person-to-person close contact, possibly intimate or sexual contact,” McQuiston said.

That possibility, in turn, raises questions about how long monkeypox has been circulating outside Africa and how transmissible the virus is.

“This is like tuning in to a new television series and we don’t know what episode we’ve landed on,” Anne Rimoin, an epidemiology professor at UCLA Fielding School of Public Health, said. “We’re now just starting to get some of the origin story.”

Was monkeypox spreading undetected?
Nearly 900 monkeypox cases have been reported outside Africa since early May, according to, a group that gathers infectious disease data. Before that, the largest outbreak in the Western Hemisphere was 47 U.S. cases in 2003. Those people were infected by pet prairie dogs; no human-to-human transmission was documented.

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