Scientists in China studying the viral disease outbreak's origin say they have found that two main types of the new coronavirus could be causing infections.
The researchers, from Peking University's School of Life Sciences and the Institut Pasteur of Shanghai under the Chinese Academy of Sciences, cautioned that their analysis examined a limited range of data, and said follow-up analyses of larger data sets are needed to better understand the virus's evolution.
The preliminary study found that a more aggressive type of the new coronavirus associated with the disease outbreak in Wuhan accounted for about 70 percent of analysed strains, while 30 percent was linked to a less aggressive type.
The prevalence of the more aggressive virus decreased after early January 2020, they said.
"These findings strongly support an urgent need for further immediate, comprehensive studies that combine genomic data, epidemiological data, and chart records of the clinical symptoms of patients with coronavirus disease 2019 (Covid-19)," they wrote.
Their findings were published on Tuesday in the National Science Review, the journal of the Chinese Academy of Sciences.
The findings come amid a fall in new coronavirus cases following crippling restrictions imposed on the world's second largest economy to stop its spread, including transport suspensions and the extension of the Lunar New Year holiday.
Mainland China had 119 new confirmed cases of coronavirus on Tuesday, the National Health Commission said, down slightly from 125 the previous day, in a broad trend that has seen numbers of new cases fall from the middle of February.
The total number of cases on the mainland has now reached 80,270. The number of deaths rose by 38 to bring the total toll for mainland China to 2981 by 3 March.
All but one new death occurred in Hubei province, the epicentre of the outbreak.
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With the number of new daily infections overseas now exceeding new cases in China, Chinese officials have begun to seek ways to control the spread of the virus outside of China and guard against future outbreaks.
Authorities have asked overseas Chinese hoping to return home to reconsider their travel plans, while cities across the country have set up quarantine rules for those entering from high-risk places.
Italy, South Korea, and Iran have all become infection hot spots.
An infected person is known to have arrived in China from Iran last week.
China is encouraging domestic producers of medical protective equipment to export protective suits to meet overseas demand as the virus spreads, Cao Xuejun, an official with China's Ministry of Industry and Information Technology said in a press briefing in Beijing on Wednesday.
China's health authorities are also studying setting up emergency reserves for medical resources and protective materials, Mao Qunan, an official at China's National Health Commission said at the same briefing.
The coronavirus outbreak had exposed the weakness of China's emergency reserves, he said.