There have been 266 cases of whooping cough reported so far this year in San Diego County, about five times more than the same period last year.

County officials say the numbers mean the region could be headed for “the worst year for the disease” since the 2010 epidemic. In that outbreak 10 infants died in California, two were from San Diego County.

An inewsource investigation that same year found the whooping cough vaccine was failing at an alarming rate, prompting several state and national studies. Whooping cough is an upper respiratory illness that can mimic a bad cold, but in infants it can be fatal. Ten new cases of the disease were reported this week in the county — all were people with up-to-date immunizations.

Joanne Faryon is a freelance reporter and former inewsource and KPBS reporter.