What if your kid makes mine sick?

It's the blunt question lurking behind a lopsided debate between the vast majority of Canadians who vaccinate their children for measles — and the few who don't; one that takes on urgency as a new season of outbreaks and warnings begins.

So what if the choice came with a cost? What if you could sue?

It was a possibility physician and researcher Kumanan Wilson decided to explore back in 2010 with the help of (then) law student Rebecca Rodal in a paper entitled Could Parents Be Held Liable for Not Immunizing Their Children?

Spoiler alert: probably not. But their findings make for interesting reading as health authorities in the Lower Mainland put out a plea for vaccination this week following a confirmed case of measles at a Maple Ridge high school.

"It seems unfair that a parent who follows the public health recommendations suffers due to the choices of parents who have not followed these same recommendations," the paper says.

"At the same time the right of parents to make decisions on behalf of their children is integral to their role as guardians and supervisors."

'Foreseeable and identifiable harm'

To be clear, there is no indication the Maple Ridge case is the fault of a vaccine opponent.

But just four years ago, a measles outbreak linked to lack of vaccination at a Christian school in Chilliwack turned out to be the worst in B.C. in three decades.

And researchers have cited the rise of "vaccine hesitancy" going back to the 1990s as one of the reasons provinces have trouble meeting the 95 per cent target needed for herd immunity — the point at which enough people in a population have immunity through vaccination or previous exposure to effectively protect those without immunity.

It's not something doctors dwell on, but a tiny percentage of people may still get sick even with the vaccine.

The overwhelming majority of Canadians have been vaccinated for measles, an extremely contagious virus that is spread in the air through coughing and sneezing. (CBC)

Which is where the issue of blame arises if the child who gives them measles wasn't vaccinated because of philosophical or religious — as opposed to medical — grounds.

Wilson and Rodal concluded linking an infection back to one individual would be almost impossible. But in theory, a group of people could be held responsible. And sued.

And that governments should take steps to clearly let parents know their choices carry consequences.

"Exemptions should remain a personal choice," Wilson and Rodal conclude. "But they should be reframed as one that does not negate liability if it results in a foreseeable and identifiable harm."

'Never going to change their minds'

At present, Canada has a patchwork of laws governing immunization. Ontario and New Brunswick both have legislation that requires students to provide proof of vaccination before they enter school.

Ontario's Immunization of School Pupils Act grants exemptions on medical grounds.

Parents can also be exempted for "conscience or religious belief" but not until they complete an education session on — among other things — vaccine safety and community health.

B.C. Provincial Health officer Dr. Bonnie Henry would like to see a mandatory assessment of a child's immunization status when they enter the education system.

B.C. provincial health officer Dr. Bonnie Henry doesn't favour heavy-handed threats when it comes to vaccinations, but she would like to see the province require assessments when children enter the school system. (Jonathan Hayward/Canadian Press)

But she draws the line at heavy-handed laws like Australia's so-called "no jab, no play" legislation, which bans unvaccinated children from pre-school and daycare, and withholds child-care benefits from their parents.

She says less than one per cent of children in B.C. have never had any kind of vaccination.

"Those are the people who are hard-core anti-vaccine activists, and we're never going to change their minds," she says.

"But the vast majority of people who aren't up to date or whose children have not received their immunization, often they have questions and they don't know where to go for answers."

'We have to avoid going full militant'

Wilson — the co-author of the legal paper — agrees.

Now a senior scientist with the clinical epidemiology program at the Ottawa Hospital Research Institute, his team developed an immunization app that electronically stores vaccination records and reminds people when to get shots.

Like Henry, Wilson says tackling those types of logistical hurdles is important for harried parents who miss vaccinations because of record-keeping, timetables and sheer forgetfulness.

He's been fighting anti-vaccine messages since he saw them start to proliferate on YouTube more than a decade ago. The advent of social media and a climate of conspiracy has only added fuel to the fire.

It was that spirit that sparked the consideration of legal tools to hold parents responsible.

"That was the motivation and thought behind it. In a system where laws are limited, maybe civil law would have an effect," he says.

In the intervening years, an American legal scholar named Arthur Caplan also looked at the issue, sparking an angry backlash by writing that "choices about vaccinations have consequences, and sometimes, sadly, deadly consequences," and concluding there is a scientific and legal foundation for bringing charges against non-vaccinators for the harm they do.

At the end of the day, Wilson says he feels that while the threat of a court case might sway the ambivalent, they won't touch the hard-core opponents.

"This has gone ever since vaccines have been around," he says. "I think we have to avoid going full militant on this because I think that's when you start to push some of these people toward the extreme."