A new modeling study from the United Kingdom suggests that monkeypox can spread before symptoms appear, providing the first evidence that the virus can be transmitted this way, NBC News reported.

The study from the UK Health Security Agency, published Wednesday in the medical journal The BMJ, is contrary to current public health guidance about how monkeypox spreads, indicating that pre-symptomatic transmission is indeed possible and may even be relatively common.

Earlier this year, the researchers examined more than 2,700 people with monkeypox in the United Kingdom. Researchers were then able to link thirteen of those cases to the people they infected, with ten pairs exhibiting evidence of pre-symptomatic transmission. The data revealed that an estimated 53 percent of monkeypox infections could spread pre-symptomatically—some even up to four days before symptoms appear.

“There is still more work needed to understand pre-symptomatic and asymptomatic infections and what that might mean for future policies and management of the monkeypox outbreak,” Dr. Nachi Arunachalam, the monkeypox incident director at the Health Security Agency, said in a statement.

Bill Hanage, an epidemiologist with the Harvard T. H. Chan School of Public Health, said that the study shed new light on how exactly monkeypox is spreading.

“The thing is with poxviruses in general, you tend to see transmission once symptoms develop,” Hanage, who was not involved in the study, told CNN.

“For several months now, there’s been a concern, or sort of the increasing realization, that if you’re talking about transmission in sexual networks, if there’s any type of contact where pre-symptomatic transmission would be possible, that’s it,” he continued.

According to the World Health Organization (WHO), monkeypox is a viral illness that starts with flu-like symptoms and the swelling of lymph nodes, eventually progressing to rashes on the face, hands, feet, eyes, mouth, or genitals that turn into raised bumps which then become blisters. Other symptoms include painful lesions, fever, chills, headaches, muscle aches, back pain, and fatigue.

The virus is most easily spread via open contact with the sores of an infected individual, but it can also spread through contact with materials that have the virus on them, such as shared bedding and clothing.

Meanwhile, as reported by Agence France-Presse, the WHO on Tuesday confirmed that its emergency committee had determined that the ongoing monkeypox outbreak should continue to be classified as a global health emergency.

Since monkeypox began spreading six months ago beyond the West African countries where it long has been endemic, the virus has killed thirty-six people out of more than 77,000 cases across more than 100 countries, according to WHO data. The United States has seen more than 28,000 cases of the disease.

Ethen Kim Lieser is a Washington state-based Finance and Tech Editor who has held posts at Google, The Korea Herald, Lincoln Journal Star, AsianWeek, and Arirang TV. Follow or contact him on LinkedIn.

Image: Reuters.