The public has been urged to keep wearing face coverings when visiting hospitals, care homes and other health and care settings.
The appeal from the Chief Medical Officer comes with reports of a decline in wearing of face coverings by visitors.
Professor Sir Michael McBride said: “The COVID-19 Omicron variant is extremely infectious and, despite best efforts, can spread quickly in health and social care settings.
“Please remember to wear a face covering when you are visiting. The people you are coming to see may be particularly vulnerable to the virus - as may other patients or residents.
“Also, do not visit if you have symptoms of respiratory infection.”
The Chief Medical Officer added: “Wearing a face covering remains an important way to protect others, as well as yourself. Public health advice continues to encourage their use in everyday life. That also includes on public transport and in any indoor busy setting - especially if they are not well ventilated.”