In the rooms, halls, and gathering spots of the Commonwealth’s senior care sites, the coronavirus took a particularly insidious hold in the spring and early summer. Rogerson House in Jamaica Plain had the state’s first known senior care fatality. At St. Chretienne Retirement Residence in Marlborough, 22 of 31 nuns contracted the coronavirus. Sickness spread and the residents were isolated from friends and family. Since those dark days, staff members have adjusted even the most basic of routines. Today, the way of life for residents has been transformed.