Alberta Health Services hopes to get a handle on a whooping cough outbreak in southern Alberta before school starts next month. It's offering free booster clinics for kids ages 10 through 12 in its south zone until Aug. 31.

As of last Thursday, 305 cases of whooping cough have been reported in the area south of Calgary, which includes Medicine Hat and Lethbridge, and 257 of those cases have been linked to the current outbreak.

The disease can be life-threatening to babies under the age of one, and it can manifest in older children and adults as a nagging cough that persists for weeks.

Unvaccinated pockets lead to outbreaks

The south zone has more reported cases of pertussis than all the other AHS zones combined. There were 35 cases in the Calgary zone, 73 in the Edmonton zone, 131 in the central zone, and 44 in the north zone.

The south zone covers communities south of Calgary, including Pincher Creek, Lethbridge and Medicine Hat. (Alberta Health Services)

Medical health officer Dr. Karin Goodison told the Calgary Eyeopener that the south zone is more susceptible to vaccine-preventable outbreaks because of concentrated lower immunization rates there.

"What's unique about the south zone is the way it's distributed," Goodison said.

"Normally, if you have 80 per cent of the population immunized, everybody would be mixed equally together. In the south zone, we have these groups of people that are choosing not to be immunized that sit in pockets, and that makes that group more susceptible."

Goodison said most of the people affected are in the school-age population, and AHS is offering these free booster clinics to help stem the spread once kids go back to school.

Immunization clinics will be offered until Aug. 31. Appointments are required.

With files from the Calgary Eyeopener