TLDR:<p><i>"Stanford researchers are looking into the possibility that coronavirus first hit California undetected last year, much earlier than anyone realized, and was only seen at that time as a particularly nasty and early flu season.<p>As a result, the theory says, many Californians have already unknowingly been exposed to the coronavirus and have developed immunity to it.<p>To investigate that idea, researchers are testing people for antibodies that indicate a previously undiagnosed infection that was defeated by the body's immune system.<p>The Stanford researchers tested 3,200 volunteers at three testing sites in the Bay Area. They are expected to publish the conclusions of their study in several weeks."</i>