Concern is spreading among parents of school-aged children in New Brunswick after the province's Department of Health announced an outbreak of whooping cough in the capital.

William Fallon is one of those parents. His six-year-old son goes to Park Street Elementary School, one of the several schools identified where at least one student has pertussis, better known as whooping cough.

“We got a letter about a month ago in regards to it from the school,” said Fallon.

Twelve cases have now been identified in the Fredericton area.

Whooping cough is a highly contagious bacterial infection that attacks the upper respiratory system.

Initial symptoms look like a common cold or cough, but after an incubation period of one to two weeks, can develop into something worse.

“That cough can be quite severe,” said Dr. Na-Koshie Lamptey, New Brunswick’s Regional Medical Officer of Health. “They can end up having pneumonia, end up requiring a hospital stay, and, very rarely, it can be life-threatening.”

The best line of defence is the whooping cough vaccine.

Infants should receive one every two months for their first six months, as well as boosters at 18 months, four years, and 13 years of age.

Though getting the shot won't make you completely immune to the disease, infections tend to be less serious in those with vaccination history.

For Dr. Lamptey, part of the issue is that after receiving preliminary immunizations during infancy and childhood, many are not following up with booster immunizations, which are even needed for adults.

“Pertussis is a vaccine that's very good, but we do find that the protection from it does decline over time, which is why we give booster doses,” Dr. Lamptey said.

Another risk factor is how many people are getting the vaccine to start.

“When we see outbreaks of diseases that are controlled back to the floor, quite often the root cause of that is lower immunization rates,” said pharmacist Paul Bowman.

That’s a cause for concern when parents are sending their kids to school.

“It's very scary seeing it come into the big cities and the schools, and just everywhere,” said parent Joann Rector.

Said Fallon: “Whooping cough has pretty much been abolished for years, but people that are anti-vaxxers, not wanting to vaccinate their children, are not just putting themselves at risk, but also other kids.”

The Department of Health is advising those who think they're experiencing whooping cough symptoms to see a doctor, then stay at home to avoid potentially spreading the illness.

With files from CTV Atlantic’s Jessica Ng.