A British Columbia study suggests cases of heart inflammation related to COVID-19 vaccines are rare but higher than expected among young men who got a second dose of Moderna, compared with those who received Pfizer-BioNTech's vaccine.
Lead author Dr Naveed Janjua, an epidemiologist at the BC Centre for Disease Control, says the findings related to second doses for both vaccines show men between the ages of 18 and 29 were most at risk of myocarditis when they received Moderna's vaccine.
The study, published this week in the Canadian Medical Association Journal, is based on data from hospitalizations, emergency room visits and lab tests in British Columbia after more than 10 million doses of vaccines were administered to people 12 and over between December 2020 and March 2022.
The health data was used to determine if people sought care for myocarditis seven and 21 days following vaccination.
Researchers identified 99 cases of myocarditis among 10.2 million doses that were administered.
They expected to see about seven cases, most of them among females.
However the study showed 80 males developed myocarditis, versus 19 females.
Janjua says the study authors support the use of Pfizer for second shots among men aged 18 to 29, which is in line with the current recommendation for 12-to-29-year-olds by the National Advisory Committee on Immunization.
NACI has said Pfizer may be the "preferred" vaccine for booster shots among those aged 18 to 29, though authors of the BC-based study found there's little to no difference between that vaccine and Moderna's when it comes to myocarditis rates related to third doses.