Evidence to date of adverse events associated with mRNA COVID-19 vaccines are largely local reactions such as pain and swelling of the injection site, and systemic reactions of an allergic nature
Increased incidences of myocarditis and pericarditis have been observed, most often occurring in men under 30 years of age, and most often after the second dose of mRNA vaccine, with more occurrences following the Moderna COVID-19 vaccine versus Pfizer, however all cases appear to resolve
To date, there is no evidence indicating a negative effect on the immune system from the administration of multiple doses of mRNA COVID-19 vaccines
Badea, A; Reeder, B; Groot, G; Miller, L; Mueller, M. What are the harmful/adverse effects of multiple doses of COVID-19 mRNA vaccines? 2022 Feb 04, Document no.: EOC220103 RR. In: COVID-19 Rapid Evidence Reviews [Internet]. SK: SK COVID Evidence Support Team, c2022. 10 p. (CEST rapid review report).