The U.S. has nearly a third of the world's 1.5 million official COVID-19 cases, and New York, by itself, has more coronavirus cases than any single foreign country. But while the coronavirus outbreak started in Wuhan, China, in late 2019, most of the New York cases came from Europe, and the European mutation was spreading silently around the New York City area by mid-February, two separate groups of viral historians have determined, The New York Times reported late Wednesday.

Teams of geneticists at Icahn School of Medicine at Mount Sinai and the NYU Grossman School of Medicine separately studied the genomes of coronavirus samples from different groups of COVID-19 cases in New York. "The research revealed a previously hidden spread of the virus that might have been detected if aggressive testing programs had been put in place," the Times notes. As it was, New York got its first positive COVID-19 test on March 1, followed a couple of weeks later by a surge of cases.

The silent spread of the coronavirus proved devastating. It became clear the coronavirus had been circulating locally in the Seattle area when a team at the Fred Hutchinson Cancer Research Center and the University of Washington sequenced the genome of a new COVID-19 patient in late February and found it shared genetic mutation from a case detected Jan. 20, likely from Wuhan. The New York researchers started sequencing samples soon after. President Trump closed off most travel from China on Jan. 31 but did not restrict foreigners coming from Europe until March 11.

Geneticists can trace the path a virus took by studying small mutations in its genome. The variations in this new coronavirus map the history of the virus but the mutations don't seem to affect how the virus works, which is welcome news in the hunt for a vaccine. Read more about the science and the genetic history of COVID-19 at The New York Times. Peter Weber