Blundering officials sent thousands of coronavirus warning letters to the wrong addresses in a mistake "which could endanger lives".
Around 75,000 people in Wales have been identified as being at very high risk of severe illness from Covid-19 so should have received letters advising them to stay at home for 12 weeks.
But the BBC reports that 13,000 letters, from Wales' chief medical officer, went to the previous addresses of the intended recipients.
"This is a potentially disastrous mistake which could needlessly endanger lives," Plaid Cymru's local government spokeswoman Delyth Jewell told the broadcaster.
All the letters have been reissued with the Government blaming a "processing error".
A Welsh Government admitted the mistake had happened.
He said: "Due to a processing error within the NHS Wales Informatics Service (NWIS), some shielding letters were posted to a previous address, where the intended recipient had recently moved. All letters have since been reissued to the correct addresses.
"We provided all local authorities with the correct details from the start of this process, and they have been directly contacting each person involved over the past two weeks.
"Supermarkets had also received the correct addresses and have been using these to prioritise delivery slots for people shielding.
"We fully understand the concern this would have caused people and sincerely apologise for the mistake."
The coronavirus death toll figure yesterday for the UK with England, Wales, Northern Ireland and Scotland combined was 12,157.
But a higher figure is feared as the official number dues not include people who have died in care homes.
