Health officials in Oregon said they are investigating four so-called "breakthrough" cases of coronavirus that were detected in individuals two weeks after they received their second dose of vaccine. The illnesses range from asymptomatic to mild, according to a news release posted Friday.

"Such cases are not unexpected," the news release said. "Clinical trials of both vaccines presently in use included breakthrough cases. In those cases, even though the participants got COVID-19, the vaccines reduced the severity of illness."

Genome sequencing is underway, and officials expect results next week. Two of the cases are located in Yamhill County, and two others are in Lane County. Local health officials are investigating the origins of the four cases.

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Overall the state has delivered at least 677,000 first and second doses of the vaccine. On Monday, the state expanded vaccine eligibility to include residents ages 75-79 a week after those over 80 began receiving the vaccine.

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Oregon has recorded at least 2,137 COVID-19 related deaths since the pandemic began, and over 150,280 cases.