Orange County health officials met in an emergency session this week after the latest measles tally showed the number of cases in the county had rocketed in the past few weeks.
There are now 21 confirmed cases of measles in Orange County, the most of any county in California, health officials said.
The number jumped upward from seven cases less than two weeks ago.
Measles cases are up across the state and rose to 32 cases by March 14, far higher than the three reported cases from the previous year. At the time, Los Angeles County led the way with 10 cases.
Healthcare officials in Orange County warned residents to review their vaccination history and to monitor themselves for illness.
Measles is a highly contagious and potentially severe disease, causing fever, rash, cough and red, watery eyes. Officials say immunization is the best defense.
It spreads very easily by air and by direct contact with an infected person, and it is contagious from about four days before the rash appears through four days after it appears.