BISMARCK, N.D. (AP) — North Dakota corrections officials say the state’s prisons have been hit hard by the coronavirus omicron variant.

The Department of Corrections and Rehabilitation says active COVID-19 cases total 151, more than double last Friday’s total and infecting about one-tenth of the prison system population. There are three dozen more cases among prison staff.

Inmates have a choice on whether to get vaccinated for COVID-19. Vaccination rates as of Jan. 13 ranged from about 82% at the Heart River Correctional Center in Mandan to about 90% at the Missouri River Correctional Center in Bismarck. The rate at the State Penitentiary in Bismarck is about 86%.