At least 31 monkeypox have been reported in 12 U.S. states and the District of Columbia, according to CDC, but experts say many cases are likely going undetected because of testing bottlenecks.

How big is the threat from monkeypox? Here's what experts say.

Where cases stand

Worldwide, more than 1,000 monkeypox cases have been reported in 29 countries, according to CDC, including the 31 reported in the United States. As of June 2, no monkeypox deaths have been reported by the World Health Organization (WHO), and despite the current transmission, CDC says the overall risk to Americans is low.

Genetic analysis by CDC found the majority of U.S. monkeypox cases have been closely related to the outbreak in Europe. However, two cases appear to be similar to another version of the virus that infected a man in Texas last year. According to CDC, this suggests that at least two separate incidents have occurred in which the virus jumped from animals to people.

Inger Damon, director of CDC's division of high-consequence pathogens and pathology, also said the agency's findings suggest the virus may have been present for longer than has been appreciated.

"What we think that this indicates is that there are likely multiple introductions out of Nigeria at points in the recent past, and there are likely additional transmission events occurring globally," Damon said. "It does raise the question … are there reservoirs and human infections occurring in a wider area? And I think it's really a further understanding of the Middle East and East Africa as potential areas where the virus was introduced."

The findings also suggest a monkeypox outbreak will likely be difficult to contain, said Angela Rasmussen, a virologist at the University of Saskatchewan. "We don't really have a good sense of how many cases there are out there," she said.

Why monkeypox cases are likely being undercounted

Experts say given the testing bottlenecks in the United States, monkeypox cases are likely being undercounted. Currently, a specimen has to be sent to one of 74 laboratories in the United States before it's then sent to CDC for confirmatory testing.

"Every single day that we're not fixing the testing bottleneck, every single day that we're not getting on top of getting the information out to the networks that need to be aware of this, is time that we are losing in terms of that window closing on containment," said Boghuma Titanji, an assistant professor of infectious diseases at Emory University.

"The U.S. probably has as many cases as Canada or the U.K.," she added. "We're just not testing enough to be able to reliably say that there are only [31] cases. I think we need to be testing way more than we're doing."

Jennifer Nuzzo, director of Brown University's Center for Pandemic Preparedness and Response, said the current testing system in the United States works for a smaller outbreak but doesn't work for clinicians who are actively monitoring for monkeypox cases.

"This two-step process is not going to scale," she said. "This is a cumbersome process. When you have something that's spreading in ways that we're not able to see—in the sense that we're finding cases without known contacts or known links of transmission—it really feels like we're in a different mode of the response."

Ranu Dhillon, an instructor of global health at Harvard Medical School, said the testing system should be designed in a way that monkeypox testing is normalized so a wider net can be cast to catch more cases. Currently, Dhillon said a test would have to be cleared with the head of a hospital's lab.

"I think the sooner we move to normalizing, the better to lower that professional stress or awkwardness of requesting a test for something that you've never seen [before]. … You have to be able to screen widely as we learn from Covid and have a lot of tests come back negative. That's how you're going to find the ones that are positive," he said.

Where monkeypox vaccines stand

Currently, there are two vaccine options against monkeypox—one that was used to eradicate smallpox, and another made by Bavarian Nordic called Jynneos, which was approved by FDA in 2019 and has been shown to be safer than earlier vaccines. However, supplies are limited.

Many of the vaccines currently in the global supply are also older, according to Rosamund Lewis, technical lead for monkeypox at WHO, which poses potential supply problems. "Most of the vaccines in these reserves are in fact what we call first-generation vaccines, and they are from the eradication era," she said, adding that older versions of the vaccines "don't at the present time meet the standards we have today."

At one point, the United States had 28 million doses of Jynneos, but those doses have since expired, said Paul Chaplin, CEO of Bavarian Nordic. An HHS spokesperson told Axios the United States has 36,000 doses of Jynneos in its immediate inventory.

Raj Panjabi, White House senior director for global health security, said 1,200 vaccine and 100 treatment courses have been delivered to eight jurisdictions in the United States.

WHO officials last week asked countries with stockpiles of both monkeypox and smallpox vaccines to distribute those vaccines to different countries based on their need; however an HHS official said the United States has not yet decided whether it will answer WHO's call.

"Given that the current situation involves monkeypox, it is premature to comment on what steps related to this previous commitment might be taken in the current situation," an HHS official said in a statement. "No decisions have been made at this point." (Dreher, Axios, 6/7; Mandavilli, New York Times, 6/6; Branswell, STAT News, 6/3; Stobbe, Associated Press, 6/3; Branswell/Joseph, STAT News, 6/7; Payne/Mahr, PoliticoPRO [subscription required], 6/1; Doucleff, "Goats and Soda," NPR, 6/3; Scribner, Axios, 6/3; Mahr, Politico, 6/3)