Krawitt is taking action of his own. His son attends Reed Elementary in Tiburon, a school with a 7 percent PBE rate, nearly triple the statewide average. Krawitt had previously worked with the school nurse to make sure that all the children in his son's class were fully vaccinated. He said the school was very helpful and accommodating.

Now Krawitt and his wife, Jodi, have emailed the district's superintendent, requesting that the district "require immunization as a condition of attendance, with the only exception being those who cannot medically be vaccinated."

Carl Krawitt provided me with Superintendent Steven Herzog's response. Herzog didn't directly address their query, instead saying: "We are monitoring the situation closely and will take whatever actions necessary to ensure the safety of our students."

Typically, response to health emergencies rests with county health officers. During the current measles outbreak, we've already seen that unvaccinated students at Huntington Beach High School in Orange County were ordered to stay out of school for three weeks after a student there contracted measles. It's a way to contain an outbreak.

But those steps were taken in the face a confirmed case at the school.

When I called Marin County health officer Matt Willis to see what he thought of keeping unvaccinated kids out of school even if there were no confirmed cases, he sounded intrigued. "This is partly a legal question," he said.

But he was open to the idea and said he was going to check with the state to see what precedent there was to take such an action. Right now, there are no cases of measles anywhere in Marin and no suspected cases either. Still, "if the outbreak progresses and we start seeing more and more cases," Willis said, "then this is a step we might want to consider' -- requiring unvaccinated children to stay home, even without confirmed cases at a specific school.

Rhett has been treated at UCSF, and his oncologist there, Dr. Robert Goldsby, said that Rhett is likely at higher risk of complications if he were to get measles. "When your immune system isn't working as well, it allows many different infections to be worse," he said. "It's not just Rhett. There are hundreds of other kids in the Bay Area that are going through cancer therapy, and it's not fair to them. They can't get immunized, they have to rely on their friends and colleagues and community to help protect them."

Goldsby pointed to the number of people who, when facing a friend or family member who receives a challenging diagnosis, will immediately ask how they can help. "Many families will say, 'What can I do to help? What can I do to help?'" he said, repeating it for emphasis. "One of the main things they can do is make sure their [own] kids are vaccinated to protect others."

Krawitt has been speaking up about vaccination for a long time now. He told me about going to a parent meeting at his daughter's school just before the start of the school year, where a staff member reminded parents not to send peanut products to school, since a child or children had an allergy. "It's really important your kids don't bring peanuts, because kids can die," Krawitt recalls the group being told.

The irony was not lost on him. He told me he immediately responded, "In the interest of the health and safety of our children, can we have the assurance that all the kids at our school are immunized?"

He found out later from a friend that other parents who were present were "mad that you asked the question, because they don't immunize their kids."