Felician Sisters Convent in Livonia, Michigan, lost 12 of its nuns between 66 and 99 years of age between Good Friday (April 10) and May 10.
A thirteenth nun appeared to recover from Covid-19 but then died after her health deteriorated weeks later. Six other nuns contracted the infection but they survived.
The convent once was home to over 800 nuns, but its number had shrunk to just 65 sisters in recent years before the pandemic hit.
The Felician sisters insist they followed guidelines for social isolation, but their cramped circumstances and average led to the convent suffering the worst loss of life since the Spanish flu of 1918.
"We couldn't contain the grief and the sorrow and the emotional impact", she said.
"We went through the motions of doing what we had to do, but that month was like a whole different way of life.
"That was our most tragic time. It was a month of tragedy and sorrow and mourning and grieving."