"The anti-vaccine movement is very sophisticated," said Ellen Amster, chair in the history of medicine at McMaster University who studies vaccine hesitancy. "It's definitely a movement. There are people who are co-ordinated, who raise money, who buy billboards and publish children's books. They are very smart. They have celebrities. They have all these strategies to make it approachable, understandable and to make you feel you're being empowered with this information."

Public health has had to turn its messaging on its head to combat hesitancy.

"Immunization is now a topic we all discuss," said Dr. Julie Emili, a Hamilton associate medical officer of health. "I'd say 10 years ago we didn't do many interviews about immunizations. It was assumed people just get their shots. There wasn't this whole discussion about, 'Should I get my shots or shouldn't I?'"

A look at school-by-school vaccination rates in Hamilton show the potential danger the community faces as pockets of unvaccinated children cluster in the same buildings.

The Spectator requested the rates in February 2015 from the Ontario Ministry of Health and Hamilton Public Health Services. It took 18 months of negotiation before public health provided the data in August 2016 for all but the smallest Hamilton schools. It covers secondary students born in 1998 and elementary students born in 2008, which are the most recent cohorts assessed by public heath.

The data show all but one Hamilton high school and one-third of elementary schools are at increased risk of outbreak for one or more vaccine-preventable diseases because too few students are immunized.

Dozens of schools don't have what is known as herd or community immunity — where enough people are immunized to stop the spread of disease in its tracks — for potentially deadly illnesses like whooping cough, polio, measles and meningitis.

"You'll have an outbreak of some vaccine-preventable illness because there wasn't optimal herd immunity," said Bramadat, director and professor in the Centre for Studies in Religion and Society at the University of Victoria. "You have to have fairly strong herd immunity in order to protect the unvaccinated from the introduction of an active strain of some illness."

Overall vaccine exemptions are small, with fewer than 2 per cent of those born in 2005 opting out of immunization, according to a study published in the Canadian Medical Association Journal Open in September 2015.

But those with conscientious or religious objections are growing, found the research funded and conducted by Public Health Ontario with the help of the University of Toronto.

The number of kids opting out of the measles vaccine more than doubled to 1.5 per cent for those born in 2005, from 0.6 per cent for students born in 1985. At the same time, medical exemptions drastically decreased.

Ontario's Auditor General Bonnie Lysyk also warned in her 2014 report about "growing hesitancy to have children vaccinated due to concerns about the safety and effectiveness of vaccines and a sense that vaccine-preventable diseases are no longer a threat."

But it's not just the numbers that are changing, it's the fervour of the movement.

"I don't know that it's growing as much as the anti-vaxxers are intensifying," said Brian Koberlein, an astrophysicist and senior lecturer at the Rochester Institute of Technology who specializes in communicating science to the general public. "You've always had some people who were skeptical of vaccines. I think you are having more of them opt out because they are getting more entrenched in terms of what their views are."

The more evidence to the contrary you show to those opposed, the more firm they become in their opposition.

"If you have a strongly held belief and you are confronted with evidence to dispel that belief, you tend to double down and dig in your heels," said Koberlein. "That is human behaviour."

The movement has also become more vocal in recruiting others to the cause.

"It's not enough that I don't want to vaccinate myself or my kid, but I need to run out and tell you not to vaccinate your kid," said Amster.

Ellen Amster, chair in the history of medicine at McMaster University, studies vaccine hesitancy, which has seen a dramatic increase in the past two decades.

Like many health issues, socio-economics come into play, but with vaccines it's opposite the norm.

"People less likely to vaccinate tend to be higher-income and higher educated, which may throw you off a bit because you're not necessarily expecting that," said Dr. Michael Gardam, director of infection, prevention and control at Toronto's University Health Network. "Most of it is just a deeply held belief that vaccines are in some way harmful and that you simply shouldn't be getting them."

It's a conspiracy theory that starts with an increasing suspicion of the medical establishment.

"Vaccine hesitancy is a canary in the coal mine of how much trust people are putting in the public institutions that oversee scientific evidence and the experts that speak for them," said Jennifer Keelan, adjunct professor in the department of public health sciences at Concordia University of Edmonton.

"There was a time when you took a public health agency expert and put them in front of a microphone, and that was very reassuring. But there has been a counter-culture movement that is suspicious of that kind of science and bio medicine … We have to in public health cajole, plead and persuade, and that is very hard especially when the trust isn't 100 per cent there. It really comes down to trust."

Vaccine hesitancy goes hand in hand with a resurgence of naturalism, holism and alternatives to biomedicine.

"Any time you see a spike in the adoption of practices that put themselves in opposition to conventional scientific medicine, you are also going to see quite a bit of vaccine hesitancy," said Keelan. "While they are looking up information on natural ways of living, they are also going to stumble onto social media sites that are very critical of vaccines … They are a receptive audience."

A misperception that naturally-acquired immunity is best means parents don't fear their children getting the potentially deadly diseases that vaccines protect against.

"Another argument that is new is that these terrible diseases aren't really terrible," said Amster. "They're natural. Just get those diseases and you'll get your natural immunity and you'll be fine."

Chickenpox parties still exist, says Keelan, where parents purposely expose their kids to the virus.

"It's ironic that these are the same parents that will make sure there are no pesticides on their blueberries," said Keelan. "They are so concerned about that kind of a risk which is an order of magnitude smaller than any risk of an infectious disease. Our ability as humans to judge and to make risk decisions is poor."

Parents fear the immunization more than the disease despite far greater odds of a bad outcome if you get the illness than if you get the shot.

"How is there this disconnect between what typical people think and the science that is out there?" asked Dr. Jeffrey Pernica, head of pediatric infectious disease at McMaster University, while speaking at a Hamilton conference on vaccine hesitancy in May 2015.

"People don't understand probability. People tend to overestimate the likelihood of rare events and underestimate the likelihood of common events … This has massive ramifications for vaccination. People hear about very rare events and they stick in their mind. It is true influenza vaccination is associated with a one-in-one-million risk of developing this bad neurological syndrome Guillain-Barre. People remember this … And yet very commonly I would say a majority of the population thinks influenza is not a big deal even though … there are over 12,000 hospitalizations and 3,500 deaths in Canada per year."

Stories aren't told about the diseases children didn't get because they were vaccinated. What resonates are the emotional tales of self-reported adverse events from immunization.

"They're scary stories," says Emili. "Anecdotes can be very powerful and moving … That's where it's hard to counter stories that are sad, and there is a lot of emotion tied up to it with evidence that is dry."

But an event after a vaccine doesn't necessarily mean it was caused by the immunization. For example, if you come down with a cold the same day you ate an apple, it doesn't mean the fruit caused the illness.

"You have people who have either had friends or who have seen things on the Internet where parents say truthfully my kid had a vaccine, he got a fever the day after that, he was never the same and then he was diagnosed with autism," said Pernica. "But it doesn't mean the vaccine caused the autism. When you vaccinate every single child in a continent with 350 million people, sooner or later you will vaccinate somebody who starts to have the signs of autism noticed two days after the vaccine."

The risks from vaccines are actually so rare that it's hard for researchers to get high enough numbers to properly assess them.

"When these risks are one in a million, they are hard to study," said Keelan. "Vaccine-adverse events are so rare it's hard to actually say this happened because of the vaccine."

Dr. Michael Gardam, director of infection, prevention and control at Toronto's University Health Network.

One of the biggest contributors to vaccine hesitancy is society's overall lack of science literacy.

"A lot of people feel like they've got the information they need," said Emili. "They get a website or an article that seems well written, and has all this information in it, but they don't have the ability to appraise that and say is this is a good source and is this based on good evidence."

Parents do their due diligence and research vaccines ahead of their children getting them. But they have little ability to determine which studies they find online are the most reliable and what sources are credible.

"There is science that is not good which is published," said Amster. "Bad science gets passed around."

Many trying to evaluate the science don't know the difference between randomized controlled trials and observational studies. They don't know which journals are peer-reviewed.

"I'm really disturbed by the level of science literacy out there," said Keelan. "I think the public is ill-armed…We have a public that really needs to be more savvy about the information they are reading and are Googling."

The playing field isn't level as science comes up against emotion.

"They're not sharing scientific facts, they're sharing conspiracy theories," said Gardam. "In medicine we need to bring our evidence and show the clinical trials. They are not bound by any of that. It's very easy to spread misinformation. All it really takes is a story."

Again, the issue goes back to trust.

"I think the other thing at work here is the tremendous shift in our culture from authority resting in institutions and figures like a judge or a doctor, and authority resting in the individual," said Bramadat. "You might have gone to medical school and read all those journals about epidemiology, but I have a great Wi-Fi connection."

There has always been opposition to immunization.

"Anti-vaccine sentiment has been around since the first vaccines were created," said Gardam. "When the first smallpox vaccine came out people were terrified of it. We've been hearing about this for the last 200 years."

But the difference is that it is now a movement with the ability to quickly spread its message far and wide on social media often with little opposition.

"Social media in general tends to build trenches," said Koberlein. "It's very easy to filter out any opposing views and keep only those views you agree with in your circle. You can build your own cocoon."

When push comes to shove and parents have to make a decision about immunization, those who are unsure tend to hesitate.

"Parents hear from physicians (that) vaccines are important, they prevent disease and you should do this, and then they also hear from friends and the Internet, 'Watch out because all this bad stuff can happen,'" said Pernica. "So what do parents do? They do nothing. They freeze. They say, 'Let's just wait,' because that is way easier than having to make a decision.

The problem with waiting is … suddenly you have many more unvaccinated and therefore unprotected young infants who are then going to get infections that they otherwise would not have gotten."

The more unvaccinated children there are together in one area like a school, the higher the risk of outbreak.

"When there is an outbreak there is a big sea change in public opinion," said Amster. "When there is an outbreak, people are, like, vaccine time, I'm going to do this."