Epidemiologists are coming around to the view that the first confirmed case of COVID-19 in the U.S., involving a Snohomish County traveler who got sick in mid-January, may not have been the one that touched off the West Coast’s coronavirus outbreak.
- The revised scenario is based on an analysis of hundreds of virus genomes, and laid out in a research paper that hasn’t yet been peer-reviewed. University of Arizona evolutionary biologist Michael Worobey and his colleagues focused on the January case, known as WA1, as well as a viral variant that spread through Washington state in late February, known as WA2.
- An earlier analysis suggested that WA2 was a version of WA1 that mutated as it spread, leading to the conclusion that WA1 must have infected hundreds of people in the interim. The later analysis finds that scenario unlikely: Instead, WA2 seems more likely to have come into the U.S. later by a different route, via China or perhaps Canada.
- The researchers said their analysis suggests there was “an extended period of missed opportunity” when intensive testing and contact tracing could have kept the outbreak from spreading as it has. Trevor Bedford, an epidemiologist at Seattle’s Fred Hutchinson Cancer Research Center who was involved in the earlier analysis, said in a Twitter thread that he now believes he was “wrong in the original assessment of a WA1 introduction, but correct in asserting significant community spread in Washington state on Feb. 29.”
For more about the research paper posted to BioRxiv, “The Emergence of SARS-CoV-2 in Europe and the U.S.,” check out Carl Zimmer’s report in The New York Times.