Severity, length of N.B. whooping cough outbreak will depend on vaccine uptake, says expert
Dr. Lisa Barrett says it could 'peter out fairly quickly' or continue 'quite a while,' with even some deaths
New Brunswick's whooping cough outbreak could get worse before it gets better, according to an infectious diseases specialist.
Dr. Lisa Barrett, an assistant professor at Dalhousie University's School of Medicine, says a lot will depend on how many people ensure their vaccinations are up to date.
"The people who get really sick, really sick with whooping cough and sometimes die are folks who are older, particularly those greater than 75, and also very, very young infants and babies. So we want to protect those folks," she said Friday.
"If everybody has a good uptake on getting up to date with their immunity, then I predict that hopefully this will sort of peter out fairly quickly. If there's not great uptake on the vaccination part, there is a good possibility that this could go on for quite a while."
One case can lead to roughly 15 new infections if people aren't protected, said Barrett.
It's "far easier to prevent spread than to fix it afterwards."
Public Health declared a province-wide outbreak Thursday, about two months after an outbreak was initially declared on the Acadian Peninsula.
A total of 141 cases have now been confirmed, with at least one case in each of the seven health zones, said Department of Health spokesperson Sean Hatchard.
That's up from 11 cases in June and from the five-year annual average of 34.
The last province-wide outbreak was in 2012.
Multiple factors are considered when deciding to declare an outbreak, said Hatchard. These include "historical trends in disease pattern; mode of transmission, and other considerations surrounding case finding/identification or other context-specific factors," he said in an emailed statement.
Most cases among youth aged 10-19
Whooping cough, or pertussis, is a highly contagious disease that is easily transmitted, mainly through droplets from the nose, mouth and throat of an infected person.
The outbreak is affecting all age groups, but the majority of cases involve school-aged youth, according to the province's acting chief medical officer of health.
The "biggest numbers have been in our 10 to 19-year age group," said Dr. Yves Léger.
"Those are our kids that are going back to school and so to try and limit the spread that may happen there, we want to encourage kids to be up to date" on their vaccines, he said.
The free vaccine is given at two, four, and six months, followed by a booster at 18 months, another booster at age four before starting school, and in Grade 7 as a part of the school immunization program.
Among children who were eligible to start kindergarten in 2022-23 and who provided proof of immunization, about 79 per cent were up to date on their diphtheria, tetanus, pertussis vaccine, the Department of Health's September 2023 report on school immunization shows.
Among kindergarten students with incomplete proof of immunization for these illnesses, about 78 per cent were missing only the four-year-old booster dose, according to the report.
The vaccination rate among Grade 7 students was about 80 per cent, as of 2022-23, the latest year for which data is available, the department spokesperson said.
Target vaccination rate closer to 90 per cent
CBC requested the estimated whooping cough immunization rate for New Brunswick's population as a whole, and the target vaccination rate to prevent outbreaks, but did not receive a response from the department by the end of the work day Friday.
Barrett said it's "hard to give an exact number, but I can tell you the further away from 90 per cent up-to-date immunity we get with very infectious respiratory things, whether it's a virus or a bacteria, then we start to see the opportunity for outbreaks."
If the rate is 80 per cent, for example, that means 80 out of 100 people have up-to-date immunity. "That leaves you with 20 out of 100 people that may not be protected," she said.
"If every one case of pertussis or whooping cough may spread to 15 other people, then you could see that you're going to get a number of cases continuing to spread in a community."
It can take up to six weeks for vaccines to protect people in high-exposure areas, such as schools, or while travelling, Barrett said.
But they do provide some protection after two weeks, and are worth getting as soon as possible, she said.
The Department of Health did not respond to questions about whether it's planning any vaccination blitzes before school starts, or any school-based vaccination clinics to help boost immunization rates.
'Sufficient' supply
All New Brunswickers should ensure their immunization against whooping cough is up to date, especially anyone in close contact with babies and young children, said Léger.
The vaccines are "highly effective" in preventing infection and if people do get infected, in limiting the severity, he said.
The department has a "sufficient" supply of doses to meet the needs, and people don't need to worry about timing the vaccine around other vaccines, such as the upcoming fall COVID vaccine, Hatchard said.
Vaccines are available through primary care providers, such as doctors and nurse practitioners, as well as Public Health offices.
They are provided for free to eligible infants, children and youth, adults who have not previously received one in adulthood, especially if they are going to be in regular contact with an infant, and pregnant women in their third trimester, regardless of their immunization history.
"The immunity that's created by the vaccine is actually passed on to their newborns and is really effective in helping to protect them during those first few months of life before they can actually get their own vaccines and build up their own immunities," Léger said.
'100-day cough'
Although whooping can occur at any age, it is "very serious" in babies and young children, especially for those who are too young to be fully immunized.
It begins with cold-like symptoms and a mild cough and worsens during several weeks to include coughing fits, said Léger. "You cough non-stop until you basically run out of breath.
"And then at that point a lot of people actually end up catching their breath and making this very high-pitched sound. That's what we call the 'whoop,' hence the name whooping cough," he said, noting young children also sometimes vomit at the end of these coughing spells.
"So they could be quite severe and quite unpleasant," and last for "many weeks."
The respiratory infection is also known as the "100-day cough," Léger said.
He encourages anyone who suspects they might have whooping cough to get tested and seek treatment.
The antibiotics can help shorten the duration and the severity of the symptoms, he said. They can also reduce the period of contagiousness from a month or more to roughly five days, and limit the spread.
With files from CBC News Network and Rachel Cave