On Sept. 23, California reported more than 4,200 cases so far this year, putting the state on track to break a 55-year record for infections. Nine people have died - all of them infants.
Kids in Los Angeles have been lining up for booster shoots - hoping to slow down the outbreak, reports CBS News medical correspondent Dr. Jonathan LaPook.
"The fatalities in California and the babies exposed in California - in more than 50 percent of cases - they were exposed to whooping cough by a family member," said Dr. Gil Chaves of the California Department of Health.
That's what happened in Mariah Bianchi's case. In 2005 she was pregnant with her son Dylan and had a terrible cough.
"He was born healthy," said Bianchi. "He was beautiful…and he was fine. I was still really sick."
She told her pediatrician she was worried about infecting her newborn.
"When I asked her about whooping cough, she told me it was a disease of the past and she said we don't see it anymore," said Bianchi.
But that's exactly what Dylan developed. And by the time he was hospitalized, it was too late.
"In less than 48 hours he died," said Bianchi. "The doctors didn't know what they were treating."
Vaccine advocates say the current California outbreak is happening because most adults don't realize they need a booster shot.
"Of the nine children who have died, all of them are less than three months of age," said Dr. Paul Offit. "They are too young to be vaccinated, they depended on those around them to be vaccinated so they would be protected; and they were let down."
Only six percent of adults are properly vaccinated against whooping cough. Anyone who's going to be around babies should make especially sure they're up to date with all vaccines.