Vaccination rates among kindergarteners in Vancouver-area schools are too low, in many cases, for the schools to benefit from "herd immunity," according to a new study by University of B.C. researchers.

Herd immunity occurs when enough people in a community are vaccinated that it's difficult for a disease to spread, offering protection to those unable to be vaccinated due to health conditions or age.

The study, published in Vaccine Reports, looked at how many kids were up-to-date with recommended vaccinations for measles, mumps, rubella, pertussis and other diseases in the 2013-14 school year in urban areas of the Vancouver Coastal Health Authority.

Rates varied widely by school and type of vaccine — from as low as 15 per cent up to 100 per cent compliance with recommended vaccinations.

The study found most schools don't have immunization rates of 90 per cent, which is generally needed for "herd immunity," said author Julie Bettinger, a researcher at UBC and the Vaccine Evaluation Centre of B.C. Children's Hospital.

"For parents … I would hope that it maybe shakes their complacency a little bit," she said.

"If I'm at a school where the coverage is coming in at 60 per cent, if someone brings measles into my school, my kid may not be protected if he's not gotten the vaccine."

Private schools lower, Richmond higher

The study was exploratory, prompted in part by vaccination discussions in the U.S. following a major measles outbreak linked to Disneyland last year.

Bettinger and her co-author looked for variations in vaccination rates by location and type of school — and found pockets of low vaccination, including the North Shore.

Private, non-religious schools had vaccination rates about 10 per cent lower than public schools, they found. (Religious private schools were not statistically different from public schools.)

One Waldorf school had such a low rate of vaccination, it had to be excluded from the analysis.

By location, Richmond schools had the highest vaccination rates of any local health area in the study, with more than 90 per cent of kids fully vaccinated.

Other areas were compared to the bar set by Richmond:

West Vancouver and Bowen Island — 30 per cent below Richmond rates.

North Vancouver — 20 per cent below Richmond.

Vancouver Downtown Eastside — 12 per cent below Richmond.

Vancouver Westside — 10 per cent below Richmond.

(The study did not provide absolute vaccination rates for schools in these areas, only their performance relative to Richmond.)

Vancouver Coastal Health says one reason Richmond's rates are so high is the strong working relationship there between family doctors and public health officials.

"They not only immunize young children but they also report their records to public health," said the health authority's Dr. Meena Dawar

"So, we're able to keep their records up to date, which really helps when we go to calculate kindergarten coverage."

Wealthy choosing not to vaccinate?

The authors drew links between the regions noted above and socio-economic status — noting both high and low ends of the spectrum had lower vaccination rates.

That kind of pattern would be consistent with earlier research in the U.S. and elsewhere, said Bettinger.

The UBC study did not look at why parents aren't vaccinating their kids, but other research suggests wealthier and poorer families can have very different reasons for not vaccinating, she said.

For families with lower socio-economic status, vaccines can be difficult to access, even though they're free.

"Actually getting the kids to a place where they can be immunized is a lot of work," said Bettinger.

"If you have a lot of other concerns — housing, food — making sure your child is up-to-date in their immunization may not be at the top of that list."

For more affluent families, other studies have shown a decision not to vaccine, based on mistrust of medical interventions, debunked notions of a link to autism, or other factors, said Bettinger.

"Rather than an access issue, it's people choosing not to vaccinate ... there's evidence out there that shows more vaccine hesitancy."

CBC News has previously reported on vaccination rates from the same year, and mapped which schools have the lowest vaccination rates for measles. You can find that map and vaccination rates for all schools here.

Explore the map to see which schools that report to the Vancouver Coastal Health authority are above and below the 95 per cent herd immunity level for measles vaccination rates.

Legend:

Red markers = schools with 0 to 55 per cent measles vaccination rates

Yellow markers = schools with 56 to 75 per cent measles vaccination rates

Blue circle = schools with 76 to 94 per cent measles vaccination rates

Green circles = schools with 95 per cent-plus measles vaccination rate rates