People in the Swansea Bay University Health Board area are being urged to stay away from A&E at Morriston Hospital with Covid staff shortages leading to "limited service" at the emergency department over the bank holiday weekend.
Scientists are warning of a January wave of infection with the peak still to come.
A statement from the health board said "A staff shortage worsened by Covid means we can only provide a limited service at Morriston ED over the bank holiday weekend.
"ED is for life-threatening illness or serious injury ONLY. Please use alternatives whenever possible."
Patients can access advice on where to access urgent care on the health board website.
Meanwhile coronavirus vaccines could be looked at on a "seasonal basis" due to emerging variants, Wales's chief medical officer has said.
He was speaking of the "great privilege" of being knighted in the New Year Honours.
Dr Frank Atherton, who has been given a knighthood for services to public health, said the past two years have been "really difficult", but added there is "great strength" in the UK making "collective decisions" to combat the virus after each UK nation imposed different rules around the Christmas and new year period.
He said his honour was a recognition of the "team effort" of all health professionals to keep people safe
In Wales, groups of a maximum of six are allowed to meet in pubs, cinemas and restaurants, while licensed premises can offer table service only.
A maximum of 30 people can attend indoor events and up to 50 can be present for outdoor events.
Other nations in the UK have taken a different approach, with the most relaxed restrictions in England.