Researchers in China say they’ve observed two strains of the novel coronavirus — one of which is reportedly much more viral than the other.

Scientists at Peking University’s School of Life Sciences and the Institut Pasteur of Shanghai have published a preliminary study in which they analyzed the genome of the novel coronavirus. Although it’s still preliminary stages and data is lacking, the study seems to have identified two different strains: the original one (which they call the S type), and a more viral, mutated version (L type).

There’s good news and bad news.

The good news is that the more aggressive version, the L type, was more common in Wuhan, and seems far less present in other areas. Furthermore, the number of cases involving the L type seems to be decreasing. This is good because it suggests that while the number of coronavirus cases continues to grow, we are mostly fighting the less aggressive version, and things could be far worse.

“Although the L type (∼70%) is more prevalent than the S type (∼30%), the S type was found to be the ancestral version. Whereas the L type was more prevalent in the early stages of the outbreak in Wuhan, the frequency of the L type decreased after early January 2020,” the study reads.

The bad news is that this means that the virus mutated at least once, and might do so again.

“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 authors continue.

The development of new strains is likely due to mutations and natural selection, the researchers wrote. Human intervention may have placed more severe selective pressure on the L type, which might be more aggressive and spread more quickly.

Meanwhile, the ancestral S type might have increased in relative frequency due to relatively weaker selective pressure.

Although the data is still preliminary and not yet confirmed, it offers an important insight into how the virus might mutate in the future and what we can expect from it.

Meanwhile, the number of new cases in China continues to drop. Mainland China had 119 new confirmed cases of coronavirus on Tuesday, the National Health Commission said, down from 125 the previous day.

However, the outbreak is far from contained as the virus seems to have established a foothold in other countries, including South Korea, Italy, and Iran.

Overall, there are still far more cases in China than in the rest of the world (approximately 80,000 out of 92,000 at the time this article was written), but that might soon change.

The study has been published in NSR.