The US will start screening at three airports for passengers with the mysterious, new virus originating in Wuhan, China that’s caused two deaths and dozens of people to fall sick with pneumonia.

On Friday, the Centers for Disease Control and Prevention and the Department of Homeland Security’s Customs and Border Protection announced the new measure, which will begin on January 17. Travelers from Wuhan to three US airports — San Francisco (SFO), New York (JFK), and Los Angeles (LAX) airports — will be screened for symptoms, such as cough and fever.

The move follows news of cases, involving travelers from Wuhan, popping up in Japan and Thailand. This week, a Chinese man in his 30s was diagnosed with the virus upon returning to Tokyo, where he lives. He’d been visiting Wuhan, the mainland Chinese city of 19 million that’s currently the center of the outbreak, according to Japan’s Ministry of Health.

That was the third case of international spread since the outbreak was announced on December 31. The other two cases were identified in Thailand. The first involved a 61-year-old Chinese woman, who had traveled to Bangkok from Wuhan. She came down with a fever on January 5, days before Chinese officials announced their finding that the outbreak is likely caused by a new coronavirus, of the same family of viruses as SARS. The second, also a Chinese woman, aged 74, arrived in Thailand on January 13, and had no relation to the first visitor who fell ill.

The big question these travelers raise — arguably the most important question about this outbreak — is whether they got the virus from another sick person. So far, a leading theory has been that the virus, called 2019-nCoV, spread directly from animals at a Wuhan food market, which has been linked to many of the cases in the outbreak. If that’s true, and 2019-nCoV isn’t yet spreading from person to person, the outbreak should burn out quickly. (Once the animal shedding the virus is identified and contained, cases should stop turning up.)

But at least two of the three travelers never visited the market. Wuhan officials have also reported evidence of viral spread within one family: a husband who worked at the market got sick, followed by his wife, who hadn’t visited the market. Together, these cases could signal that the virus indeed has the potential to spread from person to person, instead of just from an animal carrying the virus to humans, as health authorities had been suggesting.

If so, “the scope of this outbreak expands massively,” said Peter Daszak, the president of EcoHealth Alliance, a US global health research organization working in China. In the worst case, the virus could already be moving more broadly in Wuhan — and maybe further.

China is sharing information about the outbreak fast — a contrast to SARS

Because health authorities are dealing with a new virus, the picture of this outbreak — and its seriousness — is shifting rapidly, and will continue to do so in the coming days.

The outbreak was only declared on December 31. By January 9, the state broadcaster China Central Television reported that 15 of the people who had become ill tested positive for the new virus. By January 11, scientists in China shared the genetic sequence of the new virus, and the WHO applauded China’s efforts.

Read the rest of the article at Vox