According to preliminary research published in National Science Review, scientists in China have identified two strains of the COVID-19 coronavirus: an “S” strain and a more virulent “L” strain.

“Population genetic analyses of 103 [COVID-19] genomes indicated that these viruses evolved into two major types (designated L and S),” researchers wrote.

Researchers say the “S” type is the ancestral version which is evolutionarily older and less aggressive, and represented about 30% of analyzed samples. The “L” type was more prevalent (approximately 70%) in the samples and in the early stages of the Wuhan outbreak, researchers said. It “might be more aggressive and spread more quickly,” they wrote.

“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 COVID-19,” researchers concluded.

As of March 4, 94,251 cases of COVID-19 have been confirmed worldwide, including 3,214 deaths. The virus continues to spread in the United States, where 137 infections have been documented, according to CNN, including nine deaths in Washington State.

Photo Credit: CDC / C.S. Goldsmith and A. Tamin. Transmission electron microscopic image of an isolate from the first U.S. case of COVID-19, formerly known as 2019-nCoV. The spherical extracellular viral particles contain cross-sections through the viral genome, seen as black dots.