Island County Medical Officer Dr. Roger Case said late Thursday that five more cases of whooping cough have been confirmed on South and Central Whidbey Island.

Whooping cough, or pertussis, is highly contagious. Case said the number of cases is expected to rise; the total number of people with whooping cough now stands at 11.

“Five of these have no record of having been immunized for pertussis,” Case said. “This should bring into sharp focus the fallacy of ‘herd immunity’ as a reason one might consider avoiding having to become immunized.”

The first cases were reported early Thursday and involved children.

“We can expect more cases, should this reach the southern regions of Whidbey Island where immunization rates are lower than the state average,” Case added.