The Health Service Executive has urged people in high-risk categories to get vaccinated against influenza.
According to the HSE, the number of reported cases of influenza-type illness indicates that 'flu is now circulating.
The rates for the week ending 16 December was 24.9 cases per 100,000 population, which is above the threshold used to access influenza activity.
High-risk groups include over 65s, pregnant women and people with chronic illnesses.
Children or teenagers on long-term aspirin therapy and residents of nursing homes are also considered high risk.
According to the HSE, 'flu symptoms usually develop over a few hours and include a high temperature, sore muscles, dry cough, headache and sore throat.
Anyone experiencing 'flu symptoms is urged to rest, drink plenty of fluids and use over-the-counter remedies such as paracetamol.