A cluster of more than 50 pneumonia cases in China’s central city of Wuhan may be due to a newly emerging member of the family of viruses that caused the deadly SARS and MERS outbreaks, World Health Organization (WHO) said on Wednesday.

FILE PHOTO: A logo is pictured on the World Health Organization (WHO) headquarters in Geneva, Switzerland, November 22, 2017. REUTERS/Denis Balibouse

While the United Nations health agency said it needed more comprehensive information to confirm precisely the type of pathogen causing the infections, it said a new coronavirus was a possibility.

On Thursday, China’s official Xinhua news agency said preliminary lab results conducted by a team of experts showed a new type of coronavirus caused the outbreak that began in December.

Xu Jianguo, an academic at the Chinese Academy of Engineering who led the team, told Xinhua that tests on samples from patients found 15 positive results of the new coronavirus. Fifty nine cases of the pneumonia have been reported as of Sunday.

“It may take years for researchers to develop medicines and vaccines,” the Xinhua report said.

The outbreak comes ahead of the Lunar New Year holidays in late January, when many of China’s 1.4 billion people will be traveling to their home towns or abroad. The Chinese government expects passengers to make 440 million trips via rail and another 79 million trips via airplanes, officials said during a briefing on Thursday.

Wang Yang, the Chinese transport ministry’s chief engineer, said at the briefing that authorities will step up efforts to prevent the pneumonia outbreak from spreading further during the holiday period, including ensuring proper disinfection in major public transportation hubs.

Coronaviruses are a large family of viruses that can cause infections ranging from the common cold to Severe Acute Respiratory Syndrome (SARS). Some of the virus types cause less severe disease, while some - like the one that causes Middle East Respiratory Syndrome (MERS) - are far more severe.

The WHO noted that coronaviruses emerge periodically - including in 2002 to cause SARS and in 2012 to cause MERS.

It said that according to Chinese authorities, the virus behind the Wuhan cases can cause severe illness in some patients and does not appear to pass easily from person to person.

“More comprehensive information is required to confirm the pathogen, as well as to better understand the epidemiology of the outbreak, the clinical picture, the investigations to determine the source, modes of transmission, extent of infection, and the countermeasures implemented,” the WHO said.

In 2003, Chinese officials covered up a SARS outbreak for weeks before a growing death toll and rumors forced the government to reveal the epidemic. The disease spread rapidly to other cities and countries. More than 8,000 people were infected and 775 died.