PENDLETON — Thirteen inmates at the Umatilla County Jail tested positive for COVID-19 last week, according to Umatilla County Sheriff Terry Rowan.

The outbreak began when two inmates from the same housing unit tested positive on Tuesday, March 16, the same day the jail had begun offering the first COVID-19 vaccines to inmates, Rowan said.

In response to the positive tests, the jail tested the rest of the inmates in the housing unit where the two tested positive, which holds about 20 people. By the end of the week, 11 more tests came back positive. The housing unit was placed under quarantine, Rowan said

However, the 13 inmates who tested positive have shown “no symptoms whatsoever,” Rowan said.

Rowan said the jail has been following a variety of safety protocols to ensure that infection doesn’t continue to spread, including keeping the quarantined inmates in a unit where ventilation does not reach the rest of the jail. Inmates on quarantine are also allowed out of their cells only by themselves to ensure that they don’t pass on the virus.

The inmates who tested positive will be released from quarantine on March 25, Rowan said.

Rowan added that the jail has been able to avoid case spikes like this in the past by maintaining health and safety protocols.

Temperature checks and screening are conducted before people can enter the jail. The jail has also halved the number of people allowed in housing units of 40 people, Rowan said.

The case spike coincided with the jail’s first vaccine effort since Gov. Kate Brown announced in February that the state’s jail inmates would be offered the vaccine. In all, 160 inmates were offered the vaccine at the jail, but only 17 accepted, Rowan said.

Rowan said he wasn’t sure why inmates largely did not accept the vaccine. He added that the jail offered the Johnson & Johnson single-shot vaccine because the jail population “can change by 30 people in a day,” making it difficult for health officials to offer second doses two weeks later.