The chief medical officer is appealing to people to stay at home if they have flu-like symptoms, and to return to wearing masks on public transport.
Breda Smyth says this advice includes not going to a Christmas party or meeting family on Christmas Eve if they have new Covid-like symptoms.
Professor Smyth says she's 'very concerned' about a recent rise in coronavirus hospital admission.
She has asked people to make a concerted effort over the next four to six weeks to reduce transmission.
