What is the clinical evidence from this study?

Study design: Case-Control. Population: Myocarditis (n=87021). Intervention: mRNA Covid-19 vaccines (BNT162b2 or mRNA-1273) vs. Unexposed (unvaccinated or vaccinated >21 days prior). Primary outcome: Myocarditis within 7 days after the second dose of BNT162b2 (all dosing intervals) (OR 7.1, 95% CI 6.0-8.5).

September 5, 2024Open Access

Influence of mRNA Covid-19 vaccine dosing interval on the risk of myocarditis

Key Result

Longer intervals between consecutive doses of mRNA Covid-19 vaccines decreased the risk of vaccine-associated myocarditis by up to a factor of 4, especially in individuals under age 50.

Study Design

Type

Case-Control (n=87,021)

Multicenter

Yes

Structured PICO

Does a longer dosing interval between mRNA Covid-19 vaccine doses reduce the risk of myocarditis in individuals aged 12 or older?

Population

7911 cases of myocarditis aged 12 or more

Intervention

Longer dosing intervals between consecutive mRNA Covid-19 vaccine doses (primary series and booster)

Comparator

Shorter dosing intervals

Outcome

Occurrence of vaccine-associated myocarditissafety

Extending the interval between mRNA Covid-19 vaccine doses may significantly reduce the risk of vaccine-associated myocarditis, particularly in individuals under 50 years of age.

Main Result

Effect estimate: OR 7.1 (95% CI 6.0-8.5)

Limitations

Reliance on hospital admission diagnosis codes may have missed mild myocarditis cases that did not lead to hospitalization.
Incomplete identification of SARS-CoV-2 infection episodes due to undiagnosed cases or at-home testing without laboratory confirmation.
Findings apply to vaccines used until the end of 2022 and may not generalize to updated Covid-19 vaccines targeting the Omicron XBB.1.5 strain and its descendants.

Abstract

Myocarditis is the most salient serious adverse event following messenger RNA-based Covid-19 vaccines. The highest risk is observed after the second dose compared to the first, whereas the level of risk associated with more distant booster doses seems to lie in between. We aimed to assess the relation between dosing interval and the risk of myocarditis, for both the two-dose primary series and the third dose (first booster). This matched case-control study included 7911 cases of myocarditis aged 12 or more in a period where approximately 130 million vaccine doses were administered. Here we show that longer intervals between each consecutive dose, including booster, may decrease the occurrence of vaccine-associated myocarditis by up to a factor of 4, especially under age 50. These results suggest that a minimum 6-month interval might be required when scheduling additional booster vaccination. Dosing interval has been suggested as a modifier in the risk of myocarditis associated with Covid-19 mRNA vaccination. Here, the authors show that longer intervals between each consecutive dose, including booster, may decrease the occurrence of myocarditis, especially under age 50.

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