A viral infection that originated in the central Chinese city of Wuhan has been detected in Japan and Thailand, officials in those countries say.
South Korea and Vietnam have also said that they may be dealing with cases of the new form of coronavirus, which is in the same family as the severe acute respiratory syndrome (SARS) virus that caused more than 700 deaths worldwide after originating in China in 2003. Nearly 80 possible cases have also been reported in Hong Kong.
The apparent spread of the novel coronavirus comes as Chinese health officials announced that it was responsible for the deaths of two people in Wuhan. Authorities said tests confirmed 41 cases of the virus in China.
Most coronaviruses result in mild symptoms, including upper-respiratory tract infections like the common cold, according to the U.S. Centers for Disease Control and Prevention (CDC). But the classification of the disease puts it in the same family as SARS and the Middle East respiratory syndrome (MERS), both of which killed hundreds.
Chinese health officials have said there is no evidence of human-to-human transmission of the virus, though Sophia Chan, Hong Kong’s Secretary for Food and Health, cautioned on Thursday against ruling it out.
Arnold Monto, a professor in the School of Public Health at the University of Michigan, tells TIME that it may take some time to determine how the disease spreads.
“Something new may have unusual patterns for transmission,” he says.
All six known coronaviruses that have been found in humans can spread between people, Leo Poon, a virologist and SARS expert at the University of Hong Kong, tells TIME. “But what exactly the source of the virus is, what it looks like, we still don’t know,” he adds.
Coronaviruses can be spread through the air by coughing and sneezing, and through close personal contact, according to the CDC.
The outbreak comes ahead of the Chinese New Year holiday later this month—known for the world’s largest annual migration of people, with millions across China traveling home to visit their families.
The novel coronavirus has been linked to a seafood market that has been closed for sanitation since Jan. 1, and medical experts are still attempting to learn more about the illness.
Here’s what to know about the virus.
How serious is the novel coronavirus outbreak?
Two people have died in China, according to the National Health Commission and Wuhan Municipal Health Commission. The first confirmed fatality was a 61-year-old man, and the second death was of a 69-year-old man who was admitted to the hospital with abnormal renal function and severe damage to multiple organs.
According to Wuhan’s health bureau, 41 patients have been diagnosed with the virus, including 5 who were in critical condition as of Wednesday. Some of the patients operated stalls at the seafood market believed to be at the center of the outbreak. All of the patients are in quarantine, and 119 people remain under medical observation as of Thursday. The World Health Organization says symptoms include fever and difficulty breathing.
In Hong Kong, there has been a surge in demand for face masks and supplies of the N95 mask made by 3M—which was commonly worn during the SARS outbreak—had run out at many retailers, local media reported Jan. 7. The city’s authorities are urging those with fever and respiratory symptoms to wear a mask. More commuters have also been seen wearing face masks on public transportation out of what some may call an abundance of caution.
Where has the virus spread to?
Thailand and Japan have detected cases of the virus this month—authorities in both countries say that patients had visited Wuhan before falling ill.
According to Japanese health authorities, the patient, who is in his thirties, said that he had contact with a pneumonia patient while in Wuhan, but he did not visit the seafood market.
In Thailand, authorities detected a fever in a 61-year-old woman from Wuhan when she landed in the airport in Bangkok and hospitalized her the same day. On Friday, Thailand health authorities announced that a second woman from Wuhan, who has been quarantined since she arrived in the country on Monday, also had the virus.
There are also two suspected cases of the virus in Vietnam. Authorities put two Chinese visitors from Wuhan into isolation after they landed in the country on Jan. 14.
South Korea reported on Jan. 8 that a Chinese woman who had visited Wuhan on a business trip has been diagnosed with pneumonia. The 36-year-old Chinese woman went to Wuhan in mid-December and Xiamen in late December.
On Thursday, Hong Kong health authorities said that they had received reports of 78 suspected cases, all of whom had recently traveled to Wuhan. The city’s Hospital Authority said that six people remain in quarantine in stable condition.
The first possible case of the virus was reported in Wuhan on Dec. 12, the city’s health bureau says.
How are authorities responding?
Governments are stepping up precautionary measures in the wake of the outbreak. Hong Kong’s Hospital Authority has imposed shorter visiting hours at hospitals and is requiring all visitors to wear face masks. The city has also enhanced the airport’s thermal imaging system to screen the temperatures of travelers coming from Wuhan. Additional manpower has been assigned to the train station that connects the city to mainland China to carry out temperature checks.
Singapore’s Ministry of Health announced Jan. 2 that it was implementing temperature screenings for travelers arriving on flights from Wuhan, and infrared temperature screening devices have been installed at four Thailand airports that serve daily flights from Wuhan. Taiwan’s Centers for Disease Control has asked doctors and airport quarantine officials to notify the bureau of patients who have traveled to Wuhan and exhibit any symptoms.
The World Health Organization (WHO) says it is monitoring the situation and “in close contact with national authorities in China.”
On Jan. 7, the U.S. embassy issued a low-level alert for travel to Wuhan.
Chinese authorities were criticized for trying to cover up the SARS epidemic, which started in southern China, but experts say authorities have learned from their mistakes.
“I think the public health authorities in China realized that that really was not the way to handle things, that things come out eventually, that response is best when it is handled promptly,” Monto, the University of Michigan public health professor, says.
Despite the virus’ apparent spread elsewhere, China has not confirmed new cases of the virus in recent weeks. Experts say this may be due to ongoing development of testing for the new form of coronavirus.
“In the recognition of any new disease, there’s a problem in trying to be sure you’re identifying that particular disease when you don’t really have the diagnostic test,” Monto says. “When it’s a novel agent, developing a quick test takes awhile.”
Could this evolve into a large-scale outbreak like SARS?
Experts say that if the virus in Wuhan is capable of spreading easily from person to person, the outbreak is concerning and could cause a regional epidemic.
The disease appears to be less virulent than SARS—10% of those who contracted SARS in 2003 died—and that could mean that the situation will not take a more serious turn, Poon, the virologist at the University of Hong Kong, says.
There have also not been any outbreaks of the virus at hospitals, with no known cases of clinical workers getting infected. “This suggests that if there is human-to-human transmission, that the rate of it is quite low,” Poon adds.
Yuen Kwok-yung, a microbiologist at the University of Hong Kong, says there have been marked advances in scientific research and laboratory diagnostic capabilities since the SARS outbreak more than a decade and a half ago.
That Chinese scientists were able to identify the mystery disease as a coronavirus less than a month after the discovery, he says, is a positive sign.
“It is highly unlikely that this will lead to a major 2003-like epidemic,” Yuen says, “though we cannot be complacent.”
Write to Hillary Leung at hillary.leung@time.com and Amy Gunia at amy.gunia@time.com.