The novel coronavirus that has infected thousands of people across the world may have mutated at least once — meaning there may be two different types of the virus causing illnesses, a new study conducted by Chinese scientists suggests.

Scientists with Peking University’s School of Life Sciences and the Institut Pasteur of Shanghai in a preliminary study found that one strain — type “L” — of the virus was more aggressive and accounted for about 70 percent of the strains analyzed. The second — type “S” — was less aggressive and accounted for about 30 percent of analyzed strains.

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Initially, type L was more prevalent during the “early stages of the outbreak in Wuhan,” the Chinese city in Hubei province at the center of the outbreak, the researchers said. But this strain decreased “after early January 2020."

“Human intervention may have placed more severe selective pressure on the L type, which might be more aggressive and spread more quickly. On the other hand, the S type, which is evolutionarily older and less aggressive, might have increased in relative frequency due to relatively weaker selective pressure,” they noted.

The researchers found that second strain was likely caused by a mutation of the “ancestral version,” or type S in this case.

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“Although the L type (∼70%) is more prevalent than the S type (∼30%), the S type was found to be the ancestral version,” they noted.

“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),” the researchers concluded, cautioning the data available for the study was "very limited."