Some people are saying there are two strains of COVID19 and one is more deadly.
Yes there are two strains at least, but the differences are small. In any case it is only the journalists who make the claim about one being deadly, not the scientists.
https://www.newscientist.com/article/2236544-coronavirus-are-there-two-strains-and-is-one-more-deadly/
How fast can the coronavirus mutate?
https://www.livescience.com/coronavirus-mutations.html
In the study, a group of researchers in China analyzed the genomes of coronaviruses taken from 103 patients with COVID-19, the disease caused by SARS-CoV-2, in Wuhan, China, the epicenter of the outbreak. The team found differences in the genomes, which they said could be categorized into two "strains" of the coronavirus: the "L" type and the "S" type, the researchers wrote in the study, which was published Tuesday (March 3) in the journal National Science Review.
The researchers found the "L" type, which they deemed the more aggressive type, in 70% of the virus samples. They also found that the prevalence of this strain decreased after early January. The more commonly found type today is the older, "S" type, because "human intervention" such as quarantines may have reduced the ability of the "L" type to spread, researchers wrote in the paper.