Karina Top

By Melanie Starr

Infectious disease specialists across Canada are working hard to uncover adverse events following COVID-19 vaccinations and provide evidence-based safety recommendations to health-care providers and individuals. Dalhousie medical alum Dr. Karina Top (MD ’05, PGM ’08) is leading major parts of these national efforts.

“We are not just examining reports from patients and providers, we are actively surveying people to find incidents that have not already been reported,” says Dr. Top, an associate professor in the Department of Pediatrics and an infectious disease specialist at the IWK Health Centre. “This study is being run through the Canadian Immunization Research Network’s Canadian National Vaccine Safety Network, also known as CANVAS, which rigorously monitors vaccine safety here in Canada.”

Dr. Top is co-leading the Nova Scotia arm of the CANVAS-COVID study in collaboration with Dr. Jennifer Isenor in Dalhousie’s College of Pharmacy and fellow Dal Med alum Dr. Shelly McNeil (MD ’94, PGM ’97), professor and head of the Division of Infectious Diseases at Dalhousie.

Dr. Top and her colleagues across Canada are reaching out and surveying more than a million Canadians who received the COVID vaccines, to detect any adverse events that may not have been captured by patient and provider reports. They are comparing these figures to the rates of the same adverse events in a control group of unvaccinated Canadians.

“This allows us to tease out how many adverse events were most likely caused by the vaccine and how many were coincidental,” Dr. Top says, noting that it will take quite some time to unpack all of the data. “On an individual level, it is difficult to determine if a certain problem is caused by a vaccine, but on a population level, we can see the patterns.”

Dr. Top is also the lead researcher of the Canadian Immunization Research Network’s Special Immunization Clinic Network, which received $800,000 in funding from the Public Health Agency of Canada last year to gather the necessary data to inform ongoing adjustments to Canada’s COVID-19 vaccination guidelines—particularly in regards to the safest vaccine options for people who have already had an adverse event following vaccination against COVID-19.

“We work with these patients to collect detailed information about their adverse event, so we can determine the likelihood the vaccine caused the adverse event, and counsel on the potential risk of further doses and what steps can be taken to mitigate that risk,” says Dr. Top, who heads the national network of Special Immunization Clinics. “For example we work with allergists who conduct scratch tests with the vaccines or provide graded doses to make sure the

patient tolerates the small dose before giving a larger dose. This work has helped a lot of people get their second and third doses.”

While the number of adverse events following COVID vaccination may seem high at first glance—for example, 1,059 cases of myocarditis/pericarditis, 271 cases of thrombocytopenia, 881 cases of Bell’s Palsy and 336 deaths in Canada as of April 29, 2022—it is important to keep these figures in context.

“More than 34 million Canadians have been vaccinated against COVID, and more than 5.5 billion people have been vaccinated worldwide,” notes Dr. Scott Halperin, director of the Canadian Center for Vaccinology at the IWK and Dalhousie and nominated principal investigator of the Canadian Immunization Research Network. “Some of these adverse events following vaccination occur at rates of one case in 70,000 or 80,000 doses. At frequencies this rare, these events would not be detected in a clinical trial.”

Although many people who experienced an adverse event after their first dose faced a great deal of anxiety leading up to their second or third dose, Dr. Top says, “Internationally, we have seen that most people have not had a recurrence of the allergic reaction upon subsequent doses.”

“We are still analyzing the data and digging deeper,” Dr. Top says. “For example, we want to know what kinds of adverse events are most likely to recur, and what kinds of people are most likely to have adverse events. This will assist us in assessing people for boosters as we go forward.”

The quality of adverse event surveillance depends on thorough reporting to Public Health, notes Dr. Top. “Physicians who see a patient experiencing an adverse event after vaccination should report to Public Health,” she says. “Reporting of certain adverse events is mandated in most provinces.”