Two mRNA COVID-19 vaccines have been approved for use, Pfizer BioNTech (BNT162b2) and Moderna Spikevax (mRNA-1273), and as of March 20, 2022, more than 52 million doses of Pfizer and 22 million doses of Moderna have been administered in Canada, where this study was carried out. Clinical trials have shown that the vaccines are safe, and follow-up of vaccinated individuals has shown that side effects are mild and resolve on their own. However, some rare, but serious, side effects have been seen after both vaccines, mainly myocarditis (inflammation of the heart). While there have been many studies of each vaccine, few studies have been conducted to directly compare the safety of the two mRNA vaccines. The researchers in this study sought to compare the risk of myocarditis, pericarditis, and myopericarditis between the Pfizer and Moderna vaccines for COVID-19. People in the study were 18 years of age or older and had received two primary doses of the Pfizer or Moderna vaccine in British Columbia, Canada, with the second dose between January 1, 2021 and September 9, 2021. People whose first or second The vaccinations given outside British Columbia or had a history of myocarditis or pericarditis within a year before the second dose were excluded. In total, more than 2.2 million second doses of Pfizer and more than 870,000 doses of Moderna were administered. Within 21 days of the second dose, there were a total of 59 cases of myocarditis (21 Pfizer and 31 Moderna) and 41 cases of pericarditis (21 Pfizer and 20 Moderna). The researchers also looked at the rates per million doses, and the rate was 35.6 cases per million for Moderna and 12.6 per million for Pfizer — a nearly threefold increase after Moderna took over Pfizer. By comparison, the rates of myocarditis in the general population in 2018 were 2.01 per million in people under 40 and 2.2 per million in people over 40. Rates of myocarditis and pericarditis were higher with the Moderna vaccine in both men and women between 18 and 39 years of age, with the highest rates per million in men aged 18-29 years after a second dose of Moderna. According to the authors, the findings support the recommendation that certain populations receive specific vaccines to maximize benefits and minimize adverse effects.
Few population-based analyzes have been conducted to directly compare the safety of the two mRNA COVID-19 vaccines, which differ in important ways that could affect safety. Our findings have implications for mRNA vaccine development strategy, which should also take into account the self-limiting and mild nature of most myocarditis events, the benefits provided by vaccination, the higher efficacy of the Moderna vaccine against infections, and the nursing [found in prior studies]and the apparent higher risk of myocarditis after infection with COVID-19 than with mRNA vaccination.”
Naveed Janjua, MBBS, DrPH, lead study author and epidemiologist and executive director of Data and Analytics Services at the British Columbia Center for Disease Control
Limitations of the study include that it was observational, which limits the ability to determine causality between vaccination and myocarditis or pericarditis. However, temporality was ensured in the study design to limit the time studied between the vaccine dose and the diagnosis of myocarditis/pericarditis. Also, the study was based on hospital and emergency department visit data and may have missed some less severe cases. In a related editorial comment, Guy Witberg, MD, MPH, a cardiologist at Rabin Medical Center in Petah-Tikva, Israel, wrote that the study is reassuring about the vaccine’s safety, as it provides further data that myocarditis is a very rare side effect. after the two vaccines. , and is an important step toward a personalized approach to the delivery of COVID-19 vaccines. “[The study] should help stop ‘vaccine hesitancy’ due to concerns about cardiac adverse events,” Witberg said. “This is one of only a few head-to-head comparisons of the two widely used mRNA vaccines, and its results have practical policy implications: for a significant portion of the population with CVD…these data provide a strong argument for the preferential use of BNT162b2 [Pfizer] vaccine against mRNA-1273 [Moderna].” Source: American College of Cardiology
