The city of Nelson, in B.C.'s West Kootenay region, is in the grips of a whooping cough outbreak, with around 40 people diagnosed with it in the past four months.
Whooping cough, also called pertussis, is a bacterial lung infection that poses a serious risk to babies. Adults can show much milder symptoms, which can help in its spread.
Infection is preventable, as long as enough people buy into immunization, but in Nelson many parents don't.
Interior Health (IH) medical health officer Dr. Rob Parker said over a third of parents there refuse to have their children vaccinated against whooping cough.
"It's been the lowest [rate] in IH and probably the lowest in the province," he told CBC News.
Pre-school children are the group that fall ill with pertussis most often, and the infection can be debilitating and even fatal, he said.
Parker also said the pattern of outbreaks is cyclical, and far too common in Nelson and the West Kootenay.
"It's a cycle. It's a type of germ, a bacteria, that's always in peoples noses. So, if you've got vaccine-induced immunity and you keep the vaccine rates up amongst most kids, then you can generally avoid any sort of community outbreak."
Parker said it's just sheer luck that Nelson hasn't had seen a death from whooping cough this year.