The father of a California boy who is battling leukemia has asked officials at his child's school to bar unvaccinated children from attending class in the interests of his son's health, according to reports. The call comes amid a surge in the number of cases of preventable diseases in the state in recent years, as some parents choose not to vaccinate their children.

Carl Krawitt's son Rhett, 6, has been fighting leukemia for over four years, and is now in remission. But years of chemotherapy have left him susceptible to infection and unable to be vaccinated, as his immune system is still rebuilding itself. As such, he relies on "herd immunity" -- when enough members of a community have been vaccinated to effectively negate the chance of communicable diseases spreading.

“I respect people’s choices about what to do with their kids, but if someone’s kid gets sick and gets my kid sick, too, that’s a problem,” Krawitt of Corte Madera, California, told the New York Times. “What we need to do, for all our children, is increase the herd immunity.”

Marin County, California, however, where Rhett lives, has one of the highest rates of "personal belief exemptions" -- which allow parents to send their children to school without being immunized -- in the Bay Area, and one of the highest in the state. In 2013, 7.8 percent of parents in the county chose not to vaccinate their children, according to KQED.

Krawitt emailed his district's superintendent, requesting that vaccination be a condition of attendance, except in cases where children cannot be vaccinated for medical reasons. Authorities responded to his request by saying that they were “monitoring the situation closely and will take whatever actions necessary to ensure the safety of our students,” according to NPR.

California parents have a legal right to decline vaccinations for their children however, meaning that it would be illegal to bar unvaccinated children from school, according to a statement from the district's superintendent, cited by SFGate.

“California law protects the rights of parents to refuse to vaccinate their children and, in doing so, prohibits schools from excluding these children from school unless there is an active outbreak,” Reed Unified School District Superintendent Herzog wrote.

The school district's hands are, to an extent, tied by the fact that they have not had a confirmed case of measles among their students yet. The disease presents a particular risk to Rhett considering his fragile immune system. California has recently seen a measles outbreak, with around 70 cases centered around the Disneyland theme park, and a whooping cough epidemic.

Both outbreaks have been linked to the state's declining vaccination rates. In some California schools, between 60 and 70 percent of parents have filed "personal belief exemptions" to excuse their children from being vaccinated. As a result, some of the state's wealthiest neighborhoods now have vaccination rates on a par with Chad or South Sudan, according to the Atlantic Monthly.

As of January 2015, California has made the criteria to obtain a personal belief exemption more restrictive, requiring parents to meet with a medical professional to discuss the risks associated with their decision, and obtain that professional's signature.