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 at least 14 days after receiving both doses.
The Health Authority said more breakthrough cases could pop up.
"Clinical trials of both vaccines presently in use included breakthrough cases. In those cases, even though the participants got Covid, the vaccines reduced the severity of illness," the agency said in a tweet.
"Based on what we know about vaccines for other diseases and early data from clinical trials, experts believe that getting a Covid-19 vaccine may also help keep you from getting seriously ill even if you do get the virus. ... Getting as many Oregonians as possible vaccinated remains a critical objective to ending the pandemic."
The agency's announcement came the same day its health officer said there has been a decline of daily Covid-19 cases over the past several weeks. As of Friday, there were 149,576 cases in the state, according to the department's count.