L.A. health officials say the majority of people who came down with measles were unvaccinated, but would not provide specific information about each patient.
Democratic state Sen. Richard Pan of Sacramento, who authored California's vaccine law, said that people now in their early 20s have a high chance of not being vaccinated because they were young children when Wakefield appeared on "60 Minutes" in the U.S. and anti-vaccine activist Jenny McCarthy began warning of the dangers of vaccines.
"It's that generation," he said. "It's accumulated over time -- a large number of unvaccinated people."
The last big measles outbreak in L.A. County, which was in 2017, centered around unvaccinated older adolescents.
In the fall of 2011, roughly 11,500 students starting seventh grade did not have all their shots, largely because their parents said it was against their personal beliefs.
That number dropped to approximately 2,100 by the fall of 2017, in large part because of a law Pan authored barring parents from skipping vaccines because of their personal beliefs.
Sponsored Video Stories from LifeZette
But people who already crossed seventh grade in 2016 when the law took effect were grandfathered into the law and did not need to get vaccinated to complete their schooling. Kids who were in seventh grade in 2011 would be college sophomores now -- and still may not have their vaccines.
Some young adults whose parents did not vaccinate them are now choosing to get vaccinated on their own, but that is rare. Some children say they didn't know their parents didn't vaccinate them.
"Policy-wise, the approach our country has taken, and many other countries, is that we require vaccinations for school," Pan said. "What happens if someone misses that window? We haven't really developed a mechanism to go back."
In 2015, the UC system approved a regulation requiring that students be fully vaccinated before enrolling at any campus. At California universities in the past decade, there have been outbreaks of mumps, meningitis and norovirus.