A highly contagious bacterial disease is spreading in four provinces, infecting as many as 2,000 people with a violent, uncontrollable cough and killing an infant in Alberta, as public-health authorities scramble to boost their vaccination programs.

British Columbia's Fraser Valley, southern Alberta, parts of Southwestern Ontario and New Brunswick are dealing with severe outbreaks of a disease that was once on the wane – pertussis, more commonly known as whooping cough, which can be especially deadly if contracted by infants. The United States, meanwhile, appears headed for its worst year for whooping cough in more than five decades, with more than 18,000 cases reported so far.

As health authorities on both sides of the border urge parents to get their children vaccinated, and start offering free vaccine clinics for adults, the outbreaks have fuelled debate about the vaccine's effectiveness over time. The latest spread of the disease can be partially explained by parents who shun vaccinating their children. But health officials say a larger issue is at play: Children under six years need five doses of the whooping cough vaccine, with a booster in their teenage years. Routine vaccination efforts, however, have stopped by the time they reach adulthood.

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"We've got waned immunity," said Doug Sider, Ontario's acting associate medical officer of health. "We're great at emphasizing childhood vaccinations. We need to do a much better job at emphasizing adult vaccinations."

New Brunswick has more than 1,000 confirmed pertussis cases to date. Southern Alberta, which usually has one to three cases a year, has 42 confirmed cases, including a one-month-old who died last month from complications caused by whooping cough.

The grieving family of that child, Harper Whitehead, encouraged parents and children to get the vaccine to prevent similar tragedies. Harper started coughing 10 days after her birth in May. She was hospitalized when her coughing became more severe. She died in hospital.

"We, as a family, aren't looking for attention from this tragic event, but to make people aware this is a real disease," Harper's aunt, Dani Whitehead, said in a statement. "This and other diseases like it can be prevented by families being immunized."

Many infectious diseases are cyclical. Whooping cough peaks every two to five years. Babies are especially vulnerable because they haven't been fully immunized against the disease. It can lead to pneumonia, brain damage and death. Infants under six months of age represent nearly 90 per cent of all pertussis-related deaths.

Ian Gemmill, medical officer of health for Kingston, Frontenac and Lennox and Addington Public Health, said research is looking at how often adults need a booster. Public health officials, he said, then need to make a firm recommendation.

"You and I won't die from it. We will be exhausted. We will be unhappy. But," Dr. Gemmill said, "the infants will."

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In an effort to curb the current outbreak, health authorities in various parts of the country are offering free vaccination clinics for parents and caregivers of infants under one. Studies have shown that 75 per cent of infants infected with whooping cough got it from a contact at home.

"What we're trying to do is if we can get adults at any age … and give them one pertussis vaccine, then we correct that waning adult immunity and we bolster that collective immunity," Dr. Sider said.

Damian Langton, 14, knows first-hand the havoc the disease can cause. Despite being vaccinated when he was younger, he was coughing so badly earlier this month that it burst some of his blood vessels and he had bruising around his eye. "I didn't think it would be that bad," the Toronto resident said. "I was shocked to know it was whooping cough."

His father, Jerry Langton, recalls his son was "gasping for air" as he coughed. Damian is on antibiotics and the cough is less frequent. Mr. Langton has this simple advice for other parents who have children with symptoms: "Treat it as quickly as possible, and don't use anything over the counter."