Publicly funded immunization programs continue to be stricken by lower-than-recommended rates of uptake among some Canadian populations, despite potentially saving hundreds of thousands of young lives a year.

In Toronto, public health officials worry that four confirmed cases of measles — two children and two adults — could be just the beginning of a larger outbreak, particularly given the warnings by the U.S. Centers for Disease Control of a flare-up that has afflicted 102 people in 14 U.S. states.

A 95 per cent vaccination rate is required for a population to achieve the protective "herd immunity," officials say.

"We know that vaccines are very safe, and well over 95 per cent of parents [in Canada] get their children vaccinated with benefit and little harm," Dr. Vinita Dubey told CBC Radio's Matt Galloway on Metro Morning.

And yet, one elementary school in downtown Toronto, the Alpha Alternative Jr. School, had a 43.75 per cent rate of inoculation — the lowest in the city, according to a Global News investigation based on 2012 Toronto Public Health data.

"How is it that a school has a 43 per cent vaccination rate?" Galloway asked.

The answer, it turns out, is somewhat complicated by a lack of nationwide immunization regulations and provinces that allow for certain exemptions.

Philosophical exemptions

Ontario is one of only two provinces that mandate children be vaccinated in order to attend school. The other is New Brunswick. Everywhere else it is voluntary.

The Ontario Immunization of School Pupils Act requires vaccination against a range of diseases, including: diphtheria, tetanus, pertussis (also known as whooping cough), polio, measles, mumps, rubella, meningococcal disease and varicella (chickenpox).

Proof of immunization against meningococcal disease, whooping cough and chickenpox were added as requirements for the 2014-2015 academic year.

Though vaccination exemption rates have remained steady in Toronto, health officials are worried that a growing U.S. trend could make its way north. (Canadian Press)

For parents opposed to vaccinations, however, there is a loophole in the form of notarized "philosophical exemptions," Dubey said.

"You can get a medical exemption if there's a medical reason you can't receive a vaccine, or there's a philosophical or religious exemption," she said.

For parents, "there's a form that they have to get completed, they have to go in front of a commissioner of oaths and get an affidavit signed by them, and that's the legal form to be able to get an exemption."

In Ontario, the document is known as Affidavit 4897-64E, or a Statement of Conscience or Religious Belief.

New Brunswick's Policy 706 form is known as an Immunization Exemption Form for School Entry.

A right to quarantine

Since 1982, New Brunswick's reporting and diseases regulation has required proof of immunization against diphtheria, tetanus, polio, measles, mumps and rubella, as a condition for admitting a child to school.

Manitoba previously required vaccination only for measles, a spokesperson with Manitoba Health said. But all vaccinations are now "voluntary," though the province still recommends young children get their shots.

"However, if a measles case occurs in a school, a child who is not immunized may be excluded from school for a period of five to 21 days post-exposure, if deemed necessary," the spokesperson said.

The same goes for Ontario and New Brunswick, whether or not a parent obtained an exemption.

In the incident of an outbreak, both Ontario and N.B. also reserve the right to quarantine unvaccinated children, or request that they stay at home.

Penalties for failure to comply

Ontario's Immunization of School Pupils Act states that anybody who fails to comply with vaccination requirements faces fines of up to $1,000.

A medical officer of health may also order a suspension of a student for up to 20 days. This happened to about 900 Ottawa high-school students who were suspended in 2013 for failing to produce records indicating their shots were up to date.

A New Brunswick public health spokesperson said the province does not specify any fines in its policy. He added that suspensions of students would be meted out by the principal and superintendent on a case-by-case basis.

The New Brunswick policy states that "it is essential" that the principal's office keep records of which children have not been immunized, "since these students may have to be excluded from school in the event of an outbreak of a vaccine-preventable disease."

The Canadian picture

Although Unicef put Canada near the bottom of industrialized nations in 2013, with an estimated 84 per cent vaccination rate, the federal government maintains that about 95 per cent of the Canadian population is immunized.

Aside from Ontario and New Brunswick, no other provinces have mandatory immunization policies, and implementation is up to the individual provinces.

This patchwork of policies also means the breadth of immunization programs varies from province to province. For example, Newfoundland and Labrador did not start its program for pneumococcal conjugate immunization until 2005, though such a vaccine had already been offered for years in Alberta.

According to a 2011 Canadian Medical Association Journal report, vaccination rates are high in most provinces, with 93.6 per cent of New Brunswick children entering kindergarten in 2008 with their shots, and an estimated 84 to 92 per cent of Ontario students aged seven to 17 with updated immunization records in the 2009-2010 school year.

Alberta, which does not enforce vaccinations, is cited in the CMAJ report as saying that its immunization rates are "over 90 per cent" for students below Grade 2.

Manitoba's chief public health officer said overall measles vaccination rates in the province are roughly 80 per cent.

In a bid for better tracking in the event of a measles outbreak across Canada, a CMAJ editorial published last May called for a national vaccine registry "to fill Canada's information gap by improving disease surveillance" and help policy-makers "target specific groups and geographic regions" for vaccine education.

For more information on vaccination guidelines, the National Advisory Committee on Immunization has published its recommended immunization schedule on the Public Health Agency of Canada website.