Table 2.
Summary of findings for myocarditis after Moderna versus Pfizer mRNA vaccination (question 2)
| Sex | Age (years) | Data source, date; country* | Risk interval; confirmed cases (yes/no) | Incidence or reporting rate per million doses after dose two (95% CI)†¶ | Relative measures (95% CI) | Conclusion following vaccination | Certainty about conclusions using GRADE |
|---|---|---|---|---|---|---|---|
| Moderna v Pfizer (ref), dose two | |||||||
| Male | 18-29 | Vaccine Adverse Events Reporting System, 6 October;* US | 7 days | Moderna: 23.9†; Pfizer: 26.0† | — | Probably a higher incidence of myocarditis with Moderna compared with Pfizer | Moderate§,‡‡ |
| COVaxON, 4 September;* Canada | Any | Moderna: 299.5 (171.2 to 486.4); Pfizer: 35.5 (7.3 to 103.7) | — | ||||
| 18-39 | Vaccine Adverse Events Reporting System, 6 October;* US | 7 days | Moderna: 19.2†; Pfizer:16.5† | — | Probably a higher incidence of myocarditis with Moderna than with Pfizer | Moderate‡‡ | |
| Vaccine Safety Datalink, 9 October; US | 7 days | — | RD: 19.1; aRR: 2.14 (0.93 to 4.98) | ||||
| Singapore Military, 24 July; Singapore | Any | Moderna: 135.3†; Pfizer: 0 events/27 632 | — | ||||
| COVaxON, 4 September;* Canada | Any | Moderna: 144.5†; Pfizer: 19.9† | — | ||||
| 30-39 | Vaccine Adverse Events Reporting System, 6 October;* US | 7 days | Moderna: 6.7; Pfizer: 5.2 | — | Might be a little-to-no difference in the incidence of myocarditis with Moderna than with Pfizer | Low‡‡,§§ | |
| 12-39 | NIMS, 15 November,‡ UK | 7 days | Moderna: IRR=54.65 (29.74 to 100.40); Pfizer: IRR=8.05 (5.37 to 12.06) | — | Might be a higher incidence of myocarditis with Moderna than with Pfizer | Low**,§§ | |
| NIMS, 15 November;1 UK | 28 days | Moderna: IRR=16.52 (9.10 to 30.00); Pfizer: IRR=3.41 (2.44 to 4.78) | — | ||||
| ≥40 | Vaccine Adverse Events Reporting System, 6 October;* US | 7 days | Moderna: 1.52† (40-64 years); Pfizer: 0.98† (40-64 years ) | — | Probably little-to-no difference in risk of myocarditis with Moderna compared with Pfizer | Moderate§§ | |
| NIMS, 15 November;‡ UK | 7 days | Moderna: 0 events; Pfizer: IRR=0.65 (0.27 to 1.59) | — | ||||
| NIMS, 15 November;‡ UK | 28 days | Moderna: 0 events; Pfizer: IRR=0.79 (0.51 to 1.23) | — | ||||
| COVaxON, 4 September;* Canada |
Any | Moderna: 0.0 (0.0 to 35.6); Pfizer: 0.0 (0.0 to 23.3) | — | ||||
| Female | 18-29 | COVaxON, 4 September* Canada |
Any | Moderna: 69.1 (14.2 to 201.9) (18-24 years); Pfizer: 0.0 (0.0 to 50.5) (18-24 years) | — | Probably higher incidence of myocarditis with Moderna than with Pfizer | Moderate§§ |
| Vaccine Adverse Events Reporting System, 6 October;* US | 7 days | Moderna: 5.5†; Pfizer: 2.0† | — | ||||
| 18-39 | Vaccine Adverse Events Reporting System, 6 October;* US | 7 days | Moderna: 3.1†; Pfizer: 1.4† | — | Might be higher incidence of myocarditis with Moderna than with Pfizer | Low**,§§ |
|
| COVaxON, 4 September * Canada |
Any | Moderna:36.8†; Pfizer: 8.9† | — | ||||
| 30-39 | Vaccine Adverse Events Reporting System, 6 October* US |
7 days | Moderna: 0.4; Pfizer: 0.7 | — | Little-to-no difference in incidence of myocarditis with Moderna than with Pfizer | Low‡‡,§§ |
|
| 12-39 | NIMS, 15 November; UK | 7 days | Moderna: IRR=28.49 (6.22 to 130.41); Pfizer: IRR=3.11 (1.23 to 7.86) | — | Might be a higher incidence of myocarditis with Moderna than with Pfizer | Low**,‡‡ | |
| NIMS, 15 November; UK | 28 days | Moderna: IRR=7.55 (1.67 to 34.12); Pfizer: 1.37 (0.67 to 2.80) | — | ||||
| ≥40 | COVaxON, 4 September;* Canada | Any | Moderna: 0.0 (0.0 to 40.9); Pfizer: 0.0 (0.0 to 23.5) | — | Probably little-to-no difference in the incidence of myocarditis with Moderna than with Pfizer | Moderate§§ |
|
| NIMS, 15 November; UK | 7 days | Moderna: 0 events; Pfizer: IRR=0.80 (0.33 to 1.97) | — | ||||
| NIMS, 15 November; UK | 28 days | Moderna: 0 events; Pfizer: IRR=1.00 (0.64 to 1.55) | — | ||||
| Vaccine Adverse Events Reporting System, 6 October;* US | 7 days | Moderna: 0.8† (40-64 years); Pfizer: 0.74† (40-64 years) | — | ||||
Explanations for Grading of Recommendations, Assessment, Development and Evaluation (GRADE): in the plain language conclusions, we have used “probably,” “might be,” and “uncertain” to reflect level of certainty in the evidence based on GRADE of moderate, low, or very low, respectively. aRR=adjusted risk ratio. RD=risk difference.
Passive surveillance.
Weighted average across multiple age groups.
This study reported incidence rate ratios (IRRs) calculated using a self-controlled case series design. In this study design, individuals serve as their own controls and risk estimates in pre-intervention and post-intervention intervals are calculated within individuals, rather than across individuals.
Because of the large overlap in data between male patients aged 18-29 years and 18-39 years, we only downrated 18-29 years once for inconsistency despite the large differences in effects reported between studies.
Weighted averages across age groups were calculated based on contribution of each age to the review level age category.
Rated down for indirectness to whole population, based on large differences in estimates in analyses for male individuals across age groups indicating one estimate (or even a range of estimates) for all ages (for both sexes or male patients) is not credible.
Rated down for risk of bias from use of passive surveillance and lack of case verification
Rated down for inconsistency due to only one study providing estimates
Rated down for imprecision for small sample size (<10 000 per group) or very low event rate.