The comparative risk of myocarditis, pericarditis, and myopericarditis between BNT162b2 and mRNA-1273 second doses

By Bhavana KunkalikarReviewed by Danielle Ellis, B.Sc.Nov 10 2022

In a recent study published in the Journal of the American College of Cardiology, researchers assessed the risk of myocarditis or pericarditis after the coronavirus disease 2019 (COVID-19) messenger ribonucleic acid (mRNA) vaccine second doses.

Background

Few population-based evaluations have been undertaken to directly examine the safety of the two mRNA COVID-19 vaccines, mRNA-1273 and BNT162b2, which differ significantly in aspects that may affect safety. In contrast, the majority of data is derived from indirect comparisons among epidemiological studies, which are subject to influence by variables such as unequal vaccine uptake. There is a need for comparative assessments to aid decisions on vaccine rollout as well as future booster doses.

About the study

In the present study, researchers compared the risks associated with pericarditis, myocarditis, and myopericarditis between mRNA-1273 and BNT162b2 COVID-19 vaccines.

The team performed a population-based cohort analysis utilizing British Columbia COVID-19 Cohort (BCC19C) data. The BCC19C consolidates COVID-19 data sets, such as laboratory testing, the provincial immunization registry, case surveillance, and hospitalizations, along with administrative health data holdings pertaining to the population of British Columbia, such as medical visits, hospitalizations, emergency department visits, dispensations, chronic conditions, and mortality.

Eligible participants were aged over 18 years and had a record of receiving the second mRNA immunization dose with either mRNA-1273 or BNT162b2 between 1 January 2021 and 9 September 2021 in the Provincial Immunization Registry (PIR). The primary exposure considered for the study was the second mRNA vaccination dose of either COVID-19 mRNA vaccine.

Pericarditis, myocarditis, and myopericarditis diagnosis during hospitalization or emergency department visits within 21 days after the second vaccination with an mRNA vaccine were the primary outcomes of interest. The outcomes were evaluated using the International Classification of Diseases 10th Revision (ICD-10) codes. Myocarditis codes comprised I40.1 for isolated myocarditis, I40.8 for other acute myocarditis, I40.9 for acute myocarditis unspecified, and I51.4 for myocarditis unspecified. Additionally, pericarditis codes comprised I30.0 for acute nonspecific idiopathic pericarditis, I30.8 for other forms of acute pericarditis, and I30.9 for acute pericarditis, unspecified. Myopericarditis was any ICD-10 code for myocarditis or pericarditis.

Results

The study cohort included 3,204,555 participants administered two doses of either mRNA-1273 or BNT162b2 vaccine. Almost 75% of the second doses administered were of BNT162b2, and 25% were of mRNA-1273. The median ages of the two groups were comparable, with 50 and 51 years for BNT162b2 and mRNA1273, respectively. The median period between the first and second dosage administration was also comparable, with 64 and 62 days between the first and second doses of BNT162b2 and mRNA-1273, respectively. Approximately 53% of BNT162b2 vaccinees were female compared to 49.5% of mRNA-1273 vaccinees. The distribution of comorbidities was also similar across both the mRNA vaccine types.

The team noted that approximately 871,960 and 2,223,454 doses of mRNA-1273 and BNT162b2 were administered, respectively. In the 21 days after the second mRNA vaccine dose, the team observed 59 cases of myocarditis, including 31 mRNA-1273 and 28 BNT162b2 vaccinees, with 41 cases of pericarditis, including 20 mRNA-1273 and 21 BNT162b2 recipients.    mRNA-1273 had a higher rate per million doses than BNT162b2.

The cumulative incidence plot demonstrated a rapid increase in incident myocarditis between the first seven and 10 days post-second dose vaccination for both mRNA vaccines, with mRNA-1273 having a significantly higher rate. Rates of outcomes corresponding to both vaccine types were comparatively higher for men than women and peaked between 18 and 29 years. Additionally, the mRNA-1273 prevalence was higher for both males and females aged between 18 and 29 years as well as 30 and 39 years. Compared to BNT162b2, the highest rates estimated per million doses were reported in men aged between 18 and 29 years after receiving the second mRNA-1273 dose as compared to after the BNT162b2 second dose.

Compared to BNT162b2, the mRNA1273 vaccine was correlated with over two-fold higher risks of pericarditis, myocarditis, and myopericarditis. In models that assessed the interaction between covariates and vaccine types to determine whether the impact varies across different variables, the team found that the relationship between mRNA-1273 and myocarditis was considerably stronger for those aged between 18 and 39 years, but not for those aged over 40 years. In contrast, the link between pericarditis and mRNA-1273 was observed in both gender and age groups.

Conclusion

The study findings showed that incidences of myocarditis and pericarditis following the administration of mRNA COVID-19 vaccines are uncommon. However, those who received the mRNA-1273 vaccine were at a two- to three-fold higher risk than BNT162b2. The incidence of myocarditis following administration of mRNA-1273 was highest in men aged between 18 and 39 and does not appear to be evident in older men. The researchers believe that the present findings might affect vaccine policies with respect to the selection of available vaccines.