Alberta will open mass immunization clinics this week in four communities to deal with a surge of flu cases.

As of Friday, Alberta Health Services says there were 662 confirmed flu cases in the province, including 621 people with the H1N1 form of the virus.

Alberta Health Services says the clinics are to open Thursday in Calgary and Slave Lake, and on Friday in Edmonton and Grande Prairie.

If the surge continues, more mass immunization clinics could open.

Dr. Gerry Predy, senior medical officer of health, says Albertans can get a free flu shot at the clinics, pharmacies or family physician offices.

Predy has said this H1N1 strain has been around for about five years, and hits people in their 30s, 40s and 50s harder than seniors, who usually get sick from other strains.