Four people in Oregon have tested positive for the coronavirus after receiving both doses of the Covid-19 vaccine, health officials said. There are two cases each in Yamhill and Lane counties, the state's Health Authority said in a series of tweets on Friday. The cases are either mild or asymptomatic. "We are working with our local and federal public health partners to investigate and determine case origin," the agency said. "Genome sequencing is underway, and we expect results next week." The agency referred to the individuals who tested positive as "breakthrough cases," meaning that they got sick with the virus...