Hundreds of thousands of people in the U.S. — mostly babies and toddlers — were coming down with whooping cough each year when vaccines against “this menace,” as one newspaper called it, were introduced in the 1930s and 1940s.

“Childhood Cough Is Given Knockout Blow,” the Chicago Daily Tribune announced in 1940, and within the next 40 years reported cases of whooping cough would dwindle to about 1,000 nationwide. A childhood scourge for centuries, this sometimes fatal disease seemed destined to become little more than a memory in the U.S.

But in recent years, the number of reported cases of whooping cough, also known as pertussis, has resurged.

By the end of 2011, Illinois healthcare providers had reported nearly 1,400 cases of the illness, according to the Illinois Department of Public Health. A decade before, they had reported only 194 cases. Ten years before that, the number of reported cases was only 74.

The Chicago suburbs were particularly hard hit last year. The McHenry County health department reported more than 270 cases by Dec. 31, and the DuPage County Health Department and Cook County Department of Public Health, which covers much of suburban Cook, reported more than 250 cases each. The Chicago Department of Public Health reported 79 cases. All of these numbers likely underestimate how many people are being sickened by the disease.

Why, at a time of high vaccination rates among schoolchildren, does whooping cough appear to be coming back? And why are the victims older, for the most part, than those who became ill in the pre-vaccine era?

Researchers say there is evidence that clusters of unvaccinated children play a role.

But another factor lies in the history of whooping cough vaccines.

The vaccine children receive today is different from the ones introduced 70 years ago. Some of the original immunizations were “whole-cell” vaccines, made from killed whole cells of the bacterium that causes whooping cough.