The mandate is so serious, some school districts have pulled non-complying students out of class.
At Oakland High School, district nurses spent the day administering booster shots to students who still needed it. There are still hundreds of students out there who haven't received the shot, even though the district -- at this point -- has reached an 85 percent compliance rate.
Oakland High senior Aurie Ortiz is among 1,900 students who still needed the Tdap, or whooping cough booster, before the state-mandated deadline.
"It didn't hurt at all," Ortiz said, adding that she felt it was important to get the shot "so that we can all be healthy and not get sick."
A new state law requires students get the shot within 30 days of the start of school. In Oakland, that deadline is September 30.
District Health Director Joanna Locke says there have been a handful of cases of whooping cough among students, but the larger concern is if the illness gets passed on to someone else who is especially vulnerable.
"There've been a few infant deaths in California," Locke said, "which is actually where this rule came from, and so the more people in the population that are immunized, the less risk it is to infants who have not fully had their vaccination series yet."
Mary Smith brought her two teen daughters to the Oakland High vaccination clinic on Friday. Both of her daughters attend charter schools in Oakland, and Smith was having a hard time locating an affordable place to get the vaccine so her kids can stay in class.
"Doctors offices are all jammed up," Smith said. "Walgreens wanted $65, and when I saw the ad in the Oakland Tribune for today, I made the phone call and had to rush down here."
Students who do not attend Oakland High School could still get their shot as long as they had a parental consent form.
The district is holding another clinic Monday at Skyline High School. Those students who do not get their shots by September 30 will be denied entry to school.