Three prison staffers tested positive for COVID-19 this week, the Vermont Department of Corrections said Thursday.

Two of the infected employees work at Chittenden Regional Correctional Facility in South Burlington, and the other works at Northeast Correctional Complex in St. Johnsbury, according to the state.

Only one of the South Burlington staffers was said to have worked on a prison unit near incarcerated people.

Contract tracing conducted by the state did not identify any close contacts with prisoners, and there was "minimal staff exposure," the department said in a press release. One unit inside the South Burlington prison will be tested August 11 "as a precaution."

The positive tests are the first in Vermont prisons since June. They were discovered through regular building-wide testing.

Two of the three positive staffers are vaccinated for COVID-19, department spokesperson Rachel Feldman said, including the one who worked inside the South Burlington prison unit.

Nearly 81 percent of Vermont's incarcerated population, including those housed at a private prison in Mississippi, have received COVID-19 vaccines, Feldman said. Roughly 80 percent of correctional officers have been vaccinated at clinics held for department staff. The department does not know how many officers may have gotten vaccines at other locations, Feldman said.

The new cases come as Vermont is seeing an increase in COVID-19 infections caused by the Delta variant of the virus that is affecting much of the world.

The Vermont Department of Health has reported 143 new cases since Tuesday. Eleven people were hospitalized as of Thursday, the highest number since May.