(292) The role of Rheumatic Diseases in the relationship between mRNA vaccines and Myocarditis/Pericarditis in a cohort of Italian vaccinees: TheShinISS-Vax Study

Background: Observational studies have shown that mRNA COVID-19 vaccines increase the risk of myocarditis/pericarditis (MP) in the general population, but there are no robust epidemiological studies examining the effect of rheumatic diseases (RD) on the safety profile of mRNA COVID-19 vaccines.

Objectives: This study aims to assess RD as a risk factor for MP and as a potential effect modifier on the association between mRNA COVID-19 vaccines and MP.

Methods: The study population included individuals aged ≥12 years who received the first or second dose of mRNA vaccines between 27 December 2020 and 30 September 2021. TheShinISS tool for distributed analyses, linking data from healthcare databases in five Italian regions, was used. The outcome was defined as incident cases of MP identified through emergency care visits and/or hospital admissions. RD persons were identified through hospitalizations, exemptions, or prescriptions.
RD as a risk factor for MP was estimated by Cox regression adjusted for sex, age, prescriptions, and comorbidities.
The association between first and second dose of mRNA vaccine and MP in persons with and without RD was evaluated by Self-Controlled Case Series analyses (SCCS).

Results: Among the 12 million mRNA vaccinees, 289522 (2.3%) had prior RD, and there were 1729 incident cases of MP after vaccination (median follow-up time of 270 days).
RD resulted as a risk factor for MP (adjusted HR = 1.58; 95% CI 1.31-1.92, p< 0.001).
In persons without RD, SCCS analyses showed no increased risk in the 7-day risk period after the first dose of mRNA vaccination (IR = 0.86; 95% CI 0.68-1.09), whereas an increased risk was observed after the second dose (IR = 1.57; 95% CI 1.28-1.92). Conversely, in persons with RD no increased risk was observed for both doses (first dose IR = 0.89; 95% CI 0.39-2.07; second dose IR = 0.87; 95% CI 0.35-2.15).

Conclusions: This is the first population-based SCCS analysis on the association between the mRNA vaccine and MP in RD people. Although RD emerged as a risk factor for MP, vaccination seems to not increase the risk of MP in RD persons. Further multicentric studies, considering other events of interest, are needed to evaluate the safety of COVID-19 vaccines in people with RD to inform clinical decision-making.