The study covered in this summary was published in as a preprint and has not yet been peer-reviewed.

Key Takeaways

  • People younger than 40 years and males were at elevated risk for myocarditis/pericarditis in the first 7 days after vaccination with mRNA-based COVID-19 vaccines. The risk was especially elevated after the second dose.

  • Vaccine-associated risks should be assessed in light of their efficacy in preventing serious COVID-19 disease.

Why This Matters

  • This is the first population-based active-surveillance study from Italy to investigate the association between two mRNA-based COVID-19 vaccines (Pfizer-BioNTech BNT162b2 and Moderna mRNA1273) and the risk for myocarditis/pericarditis.

  • The findings suggest that mRNA-based vaccines are associated with an increased risk for myocarditis/pericarditis in people younger than 40 years. The increased risk was moderate after vaccination with the second dose of BNT162b2 and in the youngest age group; and it was higher in males after both the first and second doses of mRNA-1273.

  • These data should be taken into consideration when weighing the overall safety and efficacy profiles of these vaccines.

Study Design

  • This population-based study involved 2,861,809 people 12 to 39 years of age who received a first dose of COVID-19 mRNA vaccine between December 27, 2020 and September 30, 2021 in four regions of Italy, representing 36% of the country’s population 12 to 39 years of age.

  • The authors used an adapted self-controlled case series design to estimate the relative incidence of myocarditis/pericarditis, which allowed for control of the participants’ time-independent characteristics.

  • The main outcome measure was the first diagnosis of myocarditis/pericarditis identified at emergency care or at hospital admission during the study period. The incidence of events in the exposure risk periods for the first and second doses were compared with the baseline period.

Key Results

  • Throughout the study period, 441 people had emergency care or hospital admission related to myocarditis/pericarditis. Of those cases, 78.5% occurred in people vaccinated with BNT162b2 and 21.5% in those vaccinated with mRNA-1273.

  • During the 21-day risk interval, 114 people developed myocarditis/pericarditis, with 64.9% of the cases occurring in those vaccinated with BNT162b2 and 35.1% in those vaccinated with mRNA-1273, for relative incidences (RIs) of 1.27 (95% CI, 0.87 – 1.85) and 2.16 (95% CI, 1.50 – 3.10) after the first and second doses, respectively.

  • Overall, the risk for myocarditis/pericarditis was elevated from days 0 to 7 after both the first (RI, 6.55; 95% CI, 2.73 – 15.72) and second (RI, 7.59; 95% CI, 3.26 – 17.65) doses of mRNA-1273, whereas an elevated risk was observed for BNT162b2 only after the second dose (RI, 3.39; 95% CI, 2.02 – 5.68).

  • In males, an elevated risk for myocarditis/pericarditis was observed from days 0 to 7 after the first dose of mRNA-1273 (RI, 12.28; 95% CI, 4.09 – 36.83) and after the second doses of both mRNA-1273 (RI, 11.91; 95% CI, 3.88 – 36.53) and BNT162b2 (RI, 3.45, 95% CI, 1.78 – 6.68).

  • Females showed an elevated risk from days 0 to 7 only after the second dose of BNT162b2 (RI, 3.38; 95% CI, 1.47 – 7.74); no such association was seen with mRNA-1273.

  • Among individuals 12 to 17 years and 18 to 29 years of age, there was an elevated risk for myocarditis/pericarditis from days0 to 7 after the second dose of BNT162b2: RI, 5.74 (95% CI, 1.52 – 21.72) and RI, 4.02 (95% CI, 1.81 – 8.91), respectively.

  • An elevated risk for myocarditis/pericarditis was observed in people 18 to 29 years of age from days 0 to 7 after the first (RI, 7.58; 95% CI, 2.62 – 21.94) and second (RI, 9.58; 95% CI, 3.32 – 27.58]) doses of mRNA-1273.

  • Those 30 to 39 years of age showed an elevated risk after a first mRNA-1273 dose from days 0 to 7 (RI, 6.57; 95% CI, 1.32 – 32.63]) and days 7 to 14 (RI, 5.87; 95% CI, 1.34 – 25.74).


  • Notoriety bias resulting from overdiagnosis of myocarditis/pericarditis and increased awareness of potential mRNA vaccination adverse events could have influenced some of the results.

  • Myocarditis/pericarditis diagnoses were based on hospital discharge and emergency care visit databases, which were not validated through the review of clinical records.

  • Additional data to differentiate between emergency care admission and hospital admission, as well as hospitalization length, were not collected but could possibly have allowed assessment of outcome severity.

  • The sample size was large but there was a small number of events; it was not always possible to provide robust model estimates in some subgroup analyses.


  • The study did not receive commercial funding but was supported by funding from the Italian Medicines Agency (AIFA) in the framework of the collaboration agreement Effectiveness and safety of COVID-19 vaccines: cohort and self-controlled case series studies.

  • None of the authors reported relevant financial relationships.

This is a summary of a preprint research study Post-marketing active surveillance of myocarditis and pericarditis following vaccination with COVID-19 mRNA vaccines in persons aged 12-39 years in Italy: a multi-database, self-controlled case series study, written by researchers at the Istituto Superiore di Sanita (National Institute of Health), the Agenzia Italiana del Farmaco (Italian Medicines Agency), the Lazio Regional Health Service, Data Science e Data Analysis, the Azienda Regionale di Coordinamento per la Salute, the Veneto Tumour Registry, the Epidemiology Observatory, the Institute of Pharmacology at the Catholic University of Sacred Heart, the University Hospital in Verona, Italy, and the Friuli Venezia Giulia Region, on medRxiv provided to you by Medscape. The study has not yet been peer reviewed. The full text of the study can be found on


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