This is a summary, written by members of the CITF Secretariat, of:
Naveed Z, Li J, Naus M, García HAV, Wilton J, Janjua NZ; Canadian Immunization Research Network (CIRN) Provincial Collaborative Network (PCN) Investigators. A Population-Based Assessment of Myocarditis Following mRNA COVID-19 booster Vaccination Among Adult Recipients. Int J Infect Dis. 2023 Mar 24:S1201-9712(23)00106-6. doi: 10.1016/j.ijid.2023.03.027.
The results and/or conclusions contained in the research do not necessarily reflect the views of all CITF members.
A CITF-funded study published in the International Journal of Infectious Diseases reaffirmed that myocarditis following an mRNA COVID-19 vaccine is rare. Furthermore, the myocarditis rate following a third mRNA dose is lower than after the second dose.
There was no association detected between the type of mRNA COVID-19 booster vaccine and myocarditis. The study was led by Dr. Zaeema Naveed (University of British Columbia) with CITF funding awarded through Dr. Jeff Kwong, on behalf of the Canadian Immunization Research Network (CIRN) Provincial Collaborative Network (PCN) investigators.
- A total of 2,299,909 booster doses of an mRNA vaccine (1,057,096 Pfizer and 1,242,813 Moderna), were administered over the study period.
- 14 cases of myocarditis were observed following the booster doses;
- 62 after the second dose;
- 4 after the first dose.
- Although the myocarditis rate among males following a third dose was slightly higher for the Pfizer vaccine (rate=8.33) than for the Moderna vaccine (rate=6.99), the difference was not statistically significant. The authors did not observe any significant differences between vaccine type and the likelihood of myocarditis within specific age groups for males or females.
- Analyses performed 21 days following vaccination found nine myocarditis cases in addition to those observed seven days post-vaccination (i.e., a total of 23 cases).
- Within the 21-day window post-third dose, the overall rate of myocarditis was 10 cases per million.
The study included adults over age 18 who received a third mRNA vaccination (Pfizer or Moderna) between December 15, 2020, and July 10, 2022 in British Columbia. Those excluded: individuals who had myocarditis a year before vaccination and residents of long-term care facilities.