Acting chief medical officer Dr Ronan Glynn has said he would be concerned if people gathered in social settings without social distancing this weekend.
All of the 23 new cases of Covid-19 that were reported yesterday occurred in people aged under 44, and 77% involved people under the age of 25.
It comes as it was confirmed that that the R number, the rate at which the Covid-19 virus is passed on, had risen to at or above 1.
Professor Phillip Nolan, of the National Public Health Emergency Team's modelling advisory group, said he was sounding a note of caution rather than one of alarm.