Observed versus expected rates of myocarditis after SARS-CoV-2 vaccination: a population-based cohort study

Abstract

As of September 2022, more than 32 million people in Canada, including around 4.5 million in British Columbia, have received a vaccine to prevent SARS-CoV-2 infection. 1 With any novel vaccine, safety and effectiveness are important to public health and may determine the success of achieving the targeted immunization coverage. According to a recent systematic review, the overall rate of SARS-CoV-2 vaccination acceptance ranges from 53.6% to 84.4% in the United States. 2 One of the key reasons for vaccine hesitancy is the fear of adverse effects. 3,4 As large populations are vaccinated, certain uncommon events may be observed that were not detected during the premarketing clinical trials, whether or not these events are related to the vaccine. The same is the case with SARS-CoV-2 vaccination. The prelicensure study data did not suggest any risk of postvaccination myocarditis. However, postmarketing studies have suggested an association between mRNA SARS-CoV-2 vaccines (BNT162b2 [Pfizer-BioNTech] and mRNA-1273 [Moderna]) and myocarditis, among other adverse events after immunization, which has raised concern regarding the safety of mRNA vaccines, specifically among younger populations. [5][6][7] Most evidence comes from case reports and case series. Earlier data have suggested higher rates of myocarditis among young adults after the mRNA-1273 compared with the BNT162b2 vaccine. Limited data are available on the rate of myocarditis after the third dose, which is relevant as further boosters are planned. Given the important economic and health consequences of COVID-19, it is vital to further evaluate the likelihood of this signal.

Booster Vaccination with SARS-CoV-2 mRNA Vaccines and Myocarditis Risk in Adolescents and Young Adults: A Nordic Cohort Study of 8.9 Million Residents

“…In another comparison of post-vaccination incidence rates and historical rates from British Columbia, Canada, a relative risk of 5.81 (95% CI, 3.83 to 8.46) was reported within a 21-day acute risk period after an mRNA booster based on 27 cases. 8 Our study adds significantly to the current evidence from analytical studies on the association between mRNA boosters and myocarditis by providing age-, sex-, and vaccine type-specific results from nationwide cohorts in the Nordic setting with free universal healthcare and complete registration of vaccinations and myocarditis hospitalizations.…”

“…6 Increased risks after the booster dose have also been observed in a French case-control study, in a US cohort of Kaiser Permanente Southern California members and in a Canadian cohort. 5,7,8 In all three studies, the relative risks associated with the booster dose were lower than the relative risks associated with the second dose.…”

“…[1][2][3][4] Currently available evidence also suggests increased myocarditis risk associated with booster doses. [5][6][7][8] In a self-controlled case series study from the UK, relative risks of 1.72 and 2.64 were observed for the 28-day risk period following a BNT or MOD booster dose vs. reference periods, respectively. 6 These relative risk estimates were lower than those observed for the 28-day period following second doses of BNT and MOD.…”

Is Covid-19 “vaccine uptake” in postsecondary education a “problem”? A critical policy inquiry

“…The literature also appeared to assume that low uptake, when driven by a reluctance to get vaccinated -rather than lack of access, or so-called "complacency" (SAGE, 2014)can neither be reasonable nor based on evidence, never mentioning peer-reviewed published evidence for the disproportionate adverse effects of Covid-19 vaccines on children, youth, and young adults, including subclinical myocarditis (Mansanguan et al, 2022;Naveed et al, 2022), "transient" reduction of sperm motility (Wesselink et al, 2022), or menstrual abnormalities (Muhaidat et al, 2022). When adverse events were mentioned as reasons for delaying or refusing vaccination, they were dismissed as "rare occurrences" warranting little concern (Lo Moro et al, 2022b) or attributed to "misinformation" .…”

In the name of health and illness: An inquiry into Covid-19 vaccination policy in postsecondary education in Canada (published https://researchandappliedmedicine.com/revistas/vol1/revista6/vacunacion-covid-ingles.pdf)

“…Importantly concerning young adults, the safety of at least some of the Covid 19 vaccines would also be called into question, as Canada, following several European countries, suspended the administration of AstraZeneca, delivered to individuals under 55, due to concerns with blood clotting (Jordans, 2021;Miller, 2021), and public health and clinical reports warned about higher than usual myocarditis and pericarditis among young adult males receiving mRNA vaccines, even as they continued encouraging vaccination for this demographic group, at most alerting the public about which brand might be less harmful (Naveed et al, 2022;Public Health Agency of Canada, 2021). Similarly, a UK government's Public Assessment Report updated in November of 2022 would revealon page 23 of its 24-pages -that due to the absence of animal studies' data on the reproductive toxicity of their leading Covid-19 vaccine (AstraZeneca), "sufficient reassurance of the safe use of the vaccine in pregnant [or breast-feeding] women could not be provided at the present time" (emphasis added), yet stopped short of discouraging vaccination in these demographic groups (UK.Gov, 2022).…”