Even after receiving two doses of COVID-19 vaccine, four people in Oregon, United States, tested positive for coronavirus, the Oregon Health Authority (OHA) informed in a series of tweets on Saturday. Two patients were in Yamhill County while the other two were in Lane County. The cases were either asymptomatic or showing mild symptoms, State Health Officer Dean Sidelinger stated.

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“As of today, we’re reporting 4 ‘breakthrough cases.’ Two are in Yamhill County and 2 are in Lane County. The illness in these individuals ranges from asymptomatic to mild. We are working with our local and federal public health partners to investigate and determine case origin,” Sidelinger said.

The announcement came the same day the health official said there has been a drop in daily COVID-19 caseload over the past several weeks. As of Saturday, there were 149,576 cases in the state, according to the department’s count.

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Sidelinger said that samples have been collected from these patients to investigate and determine case origin. “Genome sequencing is underway, and we expect results next week”

The authority said more “breakthrough cases” are expected to pop up.

Notably, another breakthrough case was reported in North Carolina and the person experienced mild symptoms.