Importance Vaccination against COVID-19 provides clear public health benefits, but vaccination also carries potential risks. National Hospital Organization Kyoto Medical Center We do not have potential conflicts of interest. Clinical studies with large cohorts involving large numbers of people are required to clarify the detailed mechanisms of the development of allergic responses after vaccination. On the other hand, the reason for the observed sex difference in the incidence of adverse events after mRNA-based COVID-19 vaccination remains unclear. The difference in the incidence of adverse events (including myocarditis and endocarditis) after vaccination with mRNA-based COVID-19 vaccine between Western countries and Japan is considered to be a characteristic of immune responses in races. Therefore, the development of myocarditis and endocarditis after vaccination is considered an acute allergic response. The onset of myocarditis and endocarditis is also observed 1 to 2 days after vaccination with vaccines other than the mRNA-based COVID-19 vaccine (i.e., polio vaccine, BCG vaccine, HPV vaccine). In other words, the results obtained from clinical studies conducted in Japan are partially different from the results obtained from clinical studies conducted in Europe and/or the United States. Furthermore, the incidence of adverse events (including anaphylactic shock) observed after vaccination with mRNA-based COVID-19 vaccine has been shown to be significantly higher in women than in Japanese men. From the results of clinical studies conducted in Japan so far, it has been reported that the incidence of adverse events (including anaphylactic shock) observed after vaccination with mRNA-based COVID-19 vaccine is about 10 times higher than in Europe and the United States. In comparison with the US results reported by Oster et al., it has been revealed that the incidence of myocarditis/endocarditis in Japanese vaccinated with mRNA-1273 vaccine (Moderna) is approximately four times higher than with BNT162b2 (Pfizer/BioNTech). In particular, Japanese young and young adult men in their teens and twenties tend to develop myocarditis and endocarditis within about four days after the second dose vaccination of the mRNA-based COVID-19 vaccine. In December 2022, results reported by the Japanese Ministry of Health, Labor and Welfare revealed that very rare cases of myocarditis and pericarditis occurred after vaccination with the mRNA-based COVID-19 vaccine from Pfizer/BioNTech or Moderna. SARS-CoV-2 Vaccination and Myocarditis in a Nordic Cohort Study of 23 Million Residents. JAMA Cardiol. 2022 7(6):600–612. That would clarify if this discordance between the two studies can be explained on the basis of length of post vaccination observation period, thus setting uniform standards for such studies in future.ġ.
follow the Nordic example and use 28 days as the follow up period. It would be interesting to see if future studies in the U.S. Most immunologically mediated cases of myocarditis occur well after 7 days following exposure to the inciting agent. However, the studies differed in the period of exposure following the vaccine, which was up to 27 days in the Nordic study versus 7 days in the present study from the United States. population shows just the opposite (between 7 to 10 per 100,000 patients who received the BNT162b2 versus about 5 per 100,000 who received the mRNA1273 vaccine).īoth studies are consistent in reporting risk of myocarditis in adolescent and young adult males, and the fact that there is a higher incidence after the second dose. In the Nordic study published in JAMA Cardiology in April 2022 the incidence of myocarditis in young adolescent and adult males aged 16 to 24 was lower in those who received the BNT162b2 vaccine (4 to 7 per 100,000 vaccinated individuals) compared to the mRNA-1273 vaccine (9 to 28 per 100,000 vaccinated individuals) (1).
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