Longer Dosing Intervals for COVID-19 mRNA Vaccines Linked to Lower Myocarditis Risk, Study Finds

COVID-19 mRNA vaccine dosing intervals significantly impact the risk of myocarditis, with longer intervals generally associated with lower risk, particularly in younger individuals and males, according to a study published in Nature Communications.

The research, which analyzed data from over 58 million people aged 12 and older between December 7, 2020, and November 30, 2022, found that the timing between vaccine doses plays a crucial role in the occurrence of this rare but serious side effect.

“We hypothesized that the variation in dose spacing, relative to the recommended schedules, that naturally occurred during the vaccination campaign could be related to a differential risk of myocarditis after each sequential dose,” explained Stephane Le Vu, PharmD, PhD, EPIPHARE Scientific Interest Group in Epidemiology of Health Products, Saint-Denis, France, and co-authors. “Probing this association could have important public health implications for the use of subsequent doses of COVID-19 or other mRNA vaccines,”

The researchers examined both the Pfizer-BioNTech (BNT162b2) and Moderna (mRNA-1273) vaccines, focusing on the primary series and first booster doses. While the risk of myocarditis increased within seven days after each dose for both vaccines, the magnitude of this risk varied significantly depending on the interval between doses.

Key findings include:

1. Shorter intervals between doses were associated with higher myocarditis risk, particularly for the second dose.
2. The highest risk was observed after a second dose of Moderna administered less than 3 weeks after the first, with an odds ratio of 34 (95% CI, 17-67).
3. For the Pfizer-BioNTech vaccine, the risk was four times lower when the second dose was given more than 7 weeks after the first, compared to less than 3 weeks.
4. The risk decreased with age, with individuals under 50, particularly males, showing the highest risk.
5. For booster doses, the risk patterns differed between the two vaccines, with Pfizer-BioNTech showing a more consistent decrease in risk with longer intervals.

“Our findings bring new evidence suggesting that longer intervals between each consecutive dose, including booster doses, may decrease the occurrence of vaccine-associated myocarditis, especially among adolescents and adults under 50,” concluded the study authors.

However, the researchers note that this approach must be balanced with the need for timely protection against COVID-19.

Reference(s) (conform to AMA style)

Le Vu S, Bertrand M, Semenzato L, et al. Influence of mRNA Covid-19 vaccine dosing interval on the risk of myocarditis. Nat Commun. 2024;15(1):7745. doi:10.1038/s41467-024-52038-6