Michigan prisons near ‘herd immunity,’ but coronavirus variant poses new threat Updated Feb 22, 2021; Posted Feb 20, 2021 Parnall Correctional Facility at 1780 E Parnall Road in Blackman Township. (J. Scott Park | Mlive.com) MLive Media GroupMLive Media Group Facebook Share Update: This story has been revised with additional information and clarification provided by MDOC spokesman Chris Gautz. Nowhere in Michigan has the prevalence of the coronavirus been as pervasive as it is among the prison population. The Michigan Department of Corrections (MDOC) responded to rampant outbreaks with ongoing mass testing that reveals infection rates approaching what medical professionals refer to as herd immunity, the level of immunity that must exist before a virus has no available hosts and can die off.