CDC this week raised its monkeypox alert to "level 2," encouraging people to practice certain safety precautions. However, a lack of information on the virus, including its primary method of transmission, has caused public confusion and may impact efforts to limit the spread of the outbreak.

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

CDC raises monkeypox alert level

According to CDC, more than 1,000 cases of monkeypox have been reported in 29 countries, with the United Kingdom seeing the highest number of cases with 302 infections.

As of June 7, the United States has reported 35 confirmed and suspected monkeypox cases across 14 states and the District of Columbia. However, experts say this number is likely an undercount due to testing bottlenecks.

"The U.S. probably has as many cases as Canada or the U.K.," said Boghuma Titanji, an assistant professor of infectious diseases at Emory University. "We're just not testing enough to be able to reliably say that there are only [35] cases. I think we need to be testing way more than we're doing."

In response to the growing number of monkeypox cases worldwide, CDC on Monday raised its monkeypox alert to "level 2," the second highest travel advisory alert from the agency. Under this advisory, travelers are recommended to "practice enhanced precautions."

Specifically, CDC advised travelers to avoid contact with individuals who are sick, including those with "skin lesions or genital lesions," as well as living or dead wild animals, such as rodents, monkeys, and apes. In addition, people who "develop new, unexplained skin rash (lesions on any part of the body), with or without fever and chills" should seek medical care.

Originally, CDC also recommended people wear face masks to reduce the spread of monkeypox, but later removed the guidance "because it caused confusion." Now, the agency says that "household contacts and health care workers," as well as others in close contact with someone with a confirmed monkeypox infection, should consider wearing masks.

Is monkeypox airborne?

According to the New York Times, CDC's turnaround on its masking recommendation for monkeypox reflects experts' incomplete understanding of the disease, particularly how it spreads.

"It's very ambiguous what the true or dominant route of transmission is, and some of that can be addressed in animal models," said Nancy Sullivan, a researcher at the National Institute of Allergy and Infectious Diseases. "Probably that needs to take a front seat for some of the laboratory research."

While experts believe monkeypox spreads primarily in close contact through skin lesions, evidence suggests the virus can also be airborne, at least over short distances. For example, during Nigeria's monkeypox outbreak in 2017, scientists recorded cases of airborne transmission within a prison and in health care workers who did not have direct contact with patients. However, it is not clear how much airborne transmission contributes to the overall spread of the virus.

So far, health officials have emphasized the role of large respiratory droplets, rather than aerosols, as the primary method of monkeypox transmission, the Times reports. According to Andrea McCollum, CDC's leading monkeypox expert, the virus requires "really close sustained contact" and is not typically "transmitted over several meters."

When asked about whether health officials should address the possibility of airborne transmission with monkeypox, McCollum said that "[i]t's a fair point to make, and it's something we certainly should consider moving forward."

In addition, Donald Milton, an expert on viruses at the University of Maryland, noted that planning for potential airborne monkeypox transmission is important, particularly in hospitals where precautions against aerosol transmission of viruses are not universal. Other health experts also said household contacts of monkeypox patients, many of whom are isolating at home, may need to take airborne transmission into consideration.

At the moment, experts say the general public's risk of monkeypox is relatively low—but it may not stay that way. According to the World Health Organization, "the overall public health risk at [a] global level is assessed as moderate" and "immediate action from countries is required to control further spread among groups at risk, prevent spread to the general population and avert the establishment of monkeypox as a clinical condition and public health problem in currently non-endemic countries." (Scribner, Axios, 6/7; Oler et al., The Hill, 6/7; Twenter, Becker's Hospital Review, 6/7; Gilchrist, CNBC, 6/8; Mandavilli, New York Times, 6/7)