The Government is urging people to get their flu shots before its subsidised campaign finishes at the end of July.
The National Influenza Strategy Group says about 1 million people have been vaccinated so far this year, but a large proportion of the population has yet to get a free shot.
The group says it has a been quiet year for flu so far, but that could change quickly as colder weather arrives over the next two months.
Pregnant women, people older than 65 and those with long-term health conditions are most at risk from the virus, it says.
