Whooping cough cases continue to increase in multiple provinces, but as kids head back to school, doctors and health-care professionals say there could be multiple factors behind the spike.
The bacterial infection, also known as pertussis, typically shows up seven to 10 days after being infected and its symptoms usually start with a mild fever, runny nose and a cough. The Public Health Agency of Canada notes that can lead to fits of coughing that can last two to eight weeks, or even up to 10 weeks, according to the U.S. Centers for Disease Control and Prevention.
Quebec is seeing the biggest jump, surpassing pre-pandemic levels with more than 11,000 cases as of last week, while New Brunswick declared an outbreak on Aug. 22 with 141 cases — exceeding the five-year average.
Dr. Isaac Bogoch, infectious diseases specialist at Toronto General Hospital, said vaccination access could be a factor.
According to Bogoch, there are some groups of people who may not have access to vaccinations through a family doctor or public health clinic; others may be choosing not to vaccinate, and there could also be people who missed a dose of a vaccine due to COVID-19 disruptions to health care.
The World Health Organization noted in a 2021 report that 3.5 million children worldwide missed their first dose of the vaccine.
But it’s not just a lack of vaccination that may be behind the surge.
Waning vaccinations, common resurgence among other causes
Bogoch and other experts said there are a few possible factors at play.
“Some of it might be related to the natural history of this particular infection where every five or six years there seems to be more of this infection around,” he said. “Some of it might be related to lower vaccine rates. Some of it might be related to waning vaccination over time.”
He adds doctors should keep an eye out for those with a prolonged or severe cough, as while it may not be pertussis, catching the case early, conducting a test and confirming the infection can help in ensuring it’s managed appropriately and does not spread.
While doctors stress the vaccine “works fairly well,” Dr. Anna Banerji, a pediatric infectious disease specialist in Toronto, told Global News that over time immunity can wane.
The formulation has also evolved over time.
“So the first thing is to make sure that the children going back to school have their vaccines up to date,” Banerji said.
Routine immunization should be provided at two, four, six and 12 to 23 months of age — usually given at 18 months — with a booster dose between four and six years and another at 14 to 16 years. As of last week, 34 per cent of Quebec’s cases were among those 10 to 14.
Dr. Earl Rubin, a pediatric infectious disease specialist in Montreal, told Global News infants are among the most susceptible so it’s wise for pregnant women in their third trimester to get a vaccine booster.
“That way the mothers will get vaccinated, mount an antibody or protection against pertussis, that antibody will cross the placenta and hopefully protect the newborn until at least the vaccination series starts at two months of age,” Rubin told Global News.
He added that adults in general should consider getting a booster as the prolonged, severe cough has been known to cause rib fractures and muscle chest pain.
Has the whooping cough vaccine changed?
The pertussis vaccine has undergone some changes over the years, which may, Rubin notes, have affected its longer-lasting immunity.
The combined diphtheria-tetanus-whole-cell pertussis vaccine was used before 1997, when a new acellular pertussis vaccine replaced it, which saw a steady decline in the incidence rate of cases, PHAC says. Incident rate refers to the number of new cases.
Rubin told Global News that the shift from a whole-cell to an acellular vaccine brought higher vaccination rates, because there are fewer adverse reactions with the newer formulation.
The whole-cell vaccine used before 1997 saw sometimes severe neurologic irritability and “difficult to control seizures.” The U.K.’s Green Book of information for physicians noted Canada saw a reduction in febrile seizures following the change.
However, Rubin noted that while the change had a positive “risk-balance benefit,” the acellular vaccine did not come with as long-lasting immunity as the previous version, leading to the need for more boosters later on.
The question of to what degree the newer vaccine formulation could be less long-lasting has been frequently discussed in medical journals as well, with some noting differing outcomes in data depending on the vaccine manufacturer and specific formulas.
“There are a number of hypotheses as to why this previously well-controlled disease is now making a resurgence. It has been suggested that the less-effective long-term protection (waning after 5–10 years) of DTaP has allowed the epidemic cycles to re-establish themselves,” noted one article in the journal Nature in September 2020.
“This is partly challenged by more recent studies that allege a long-lived, if imperfect, protection afforded by DTaP.”
A peer-reviewed article in the Canadian Medical Association Journal in 2006 also noted that the acellular vaccines might spur a need to look into more boosters to maintain immunity.
“Inactivated fractionated pertussis vaccines such as acellular vaccines were introduced into routine vaccination programs because of their improved side-effect profile and comparable immunogenicity when tested against previously used whole-cell pertussis vaccines,” the article authors noted.
“However, our results suggest that, in the short term, some acellular vaccines may not adequately provide full protection against pertussis among infants and children less than 5 years old.
“This may be a consequence of the type of immunity generated by these vaccines (i.e., higher levels of humoural immunity, or Th2-like responses). As a result, children require additional doses to reach adequate levels of immunity. Whole-cell vaccines, on the other hand, tend to elicit higher levels of cell-mediated immunity.”
However, medical experts stress that the most important thing is still to get vaccinated with whichever vaccine is available and approved where you live, and to keep up to date as needed.
The combination of close contact and out-of-date vaccines for many means cases will likely keep rising, Banerji said.
“Now that kids are going back to school and some of the kids are not completely vaccinated, I expect to see an increase,” Banerji said.
“We’ve had already huge numbers, like four times the normal rate of whooping cough that we normally see across Canada and really around the world, but I think that might even go up as kids go back to school.”
— with files from Global News’ Saba Aziz and The Canadian Press