Positive antibody tests in two Snohomish County residents indicate that COVID-19 could have possibly arrived in Washington state as far back as December.

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According to a report from The Seattle Times, a woman named Jean fell ill in December 2019, with symptoms that included a dry cough, fever, aches, and wheezing. Jean’s blood recently tested positive for the antibodies produced by a COVID infection, leading local officials to determine that it’s possible she had the illness around the time she experienced those symptoms.

Officials previously identified what they thought was the first confirmed case in both the U.S. and Washington in late-January, in a patient who had recently returned from a trip to Wuhan, China. If Jean’s serology test is accurate, that would date the arrival of the illness on American shores as even earlier than previously thought.

Antibody tests aren’t always 100% accurate, and can’t actually identify the exact time frame an infection occurred. But given Jean’s reported symptoms from December, Snohomish County officials aren’t ruling anything out for her and one other patient who tested positive.

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“They are being considered ‘probable,’” a county official spokesperson told the Times.

That being so, Snohomish County officials told KIRO 7 that there are currently no current efforts underway to reexamine the spread of COVID-19 in late 2019, citing already strained resources.

Serology testing is currently being used to determine whether people could potentially have immunity to the virus moving forward. Researchers remain uncertain, though, as to how long any sort of immunity afforded by antibodies might last.

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