Why are vaccine rates so low at some California schools? One reason is that some parents have exempted their kindergartners from vaccinations because they don't believe in them.
Another reason: parents who enroll their child on a "conditional" basis, promising that they'll catch up on the state-required vaccines at some point.
Some schools never actually follow up to ensure kindergartners get the vaccinations required by the state, according to the California Department of Public Health.
"Children may be admitted to school on the 'condition' that they complete any remaining vaccinations when due. Often there is no follow-up and these 'conditional' children remain under-vaccinated," state officials say on their Shots for School website.
That could be a reason why a school, for instance, could have 4% of kindergartners exempted from vaccines because of a parent's personal beliefs, yet only 84% of the class is vaccinated for measles.
Experts say that when the vaccination rate of a population is 92% or lower for a disease like measles, outbreaks are more likely to spread.
Schools were required to file data to the state by Oct. 15 for the incoming kindergarten class of fall 2014.
Questions and answers behind California law for vaccinating kindergartners:
Q: What does the law say about requiring vaccines for kindergartners?
A: California law requires incoming kindergartners to be vaccinated against nine diseases. All 50 states have laws requiring vaccinations for students.
Q: How is it possible to enter kindergarten without having all shots?
A: There are three ways: exemptions due to a parent's personal beliefs; exemptions for a medical reason; or a conditional admission, in which a parent is expected to bring the child's vaccinations up to date.
Q: Should schools be following up with parents to make sure their children actually get their vaccinations?
A: Yes. In fact, it's the law. "State law requires school staff to monitor these children until they are caught up," said Dr. Gil Chavez, state epidemiologist for the Department of Public Health.
"If a child has not received all immunization doses which are currently due at admission, the child should not be admitted until those doses are received or a valid exemption is submitted," Chavez said.
Q: What do other experts say?
A: Dr. James Cherry, a UCLA professor and primary editor of the Textbook of Pediatric Infectious Diseases, says schools need to do their job.
Long ago, school nurses would be in charge of ensuring vaccinations were up to date. But there has been a well-documented decline in the number of school nurses.
"School nurses have been severely cut, and a lot of the things they used to do, they simply don't do," Cherry said. "So … when something happens, then you realize how many unimmunized there are."