South Australia is experiencing a severe flu season with a reported 1700 influenza cases diagnosed so far this year, more than double at this time last year, with a 60 per cent increase in cases in the past week.

Nationally over 8,000 cases of influenza had been diagnosed.

Director of the Influenza Specialist Group, Dr Rod Pearce, said an early onset of cold and wet conditions for winter, and an uncommon strain of the flu have helped to decrease resistance.

The strain, H3N2, is the prominent type of influenza this year, and is covered by this year's flu vaccine.

"Anyone with a pre-existing illness is supported by the National Immunisation Program to get a free one, but they are not that expensive," Dr Pearce told 891 Breakfast.

Infant versions for patients over six months of age were also available.

SA chief medical officer Professor Paddy Phillips said the best way for people to protect themselves and others was to follow the mantra of 'wash, wipe and cover, don't infect another'.

Wash hands frequently, cover your mouth if you cough or sneeze (preferably with your elbow so you then do not transfer the germs onto hard surfaces), wash hands after coughing and wipe down surfaces where food is prepared.