The Ministry said the flu viruses are contagious with symptoms including fever, runny nose, dry cough, sore throat, headache, muscle and joint pain, and a general feeling of unwellness and fatigue.
It said that in June there was a surge in cases of the common flu - noticeably up on the previous two years.
The Ministry said most people recover within a week but the flu can cause severe illness or death, particularly among young children, the elderly, pregnant women, and those with serious medical conditions.