Here are some links.

Study from China that shows different strains have much different lethality with the deadlier strains in New York and Europe and milder strains in the west coast.

Antibody tests in New York and California show a much higher case fatality rate in New York:

. . . the results suggest that something like 2.7 million New Yorkers have been infected, which in turn implies a statewide infection fatality rate (IFR) in the neighborhood of 0.6 percent—three times the upper estimate from the California studies.