(343) Healthcare utilization among SARS-CoV-2 mRNA vaccine-associated myocarditis cases: a matched retrospective cohort study

Background: Health outcomes in vaccine-associated myocarditis vary, yet the long-term healthcare utilization for this condition is not fully understood.

Objectives: To evaluate all-cause healthcare utilization among those with vaccine-associated myocarditis (defined by ED visits or hospitalizations within 21 days post-SARS-CoV-2 mRNA vaccination), compared to vaccinees without post-vaccination myocarditis.

Methods: We conducted a retrospective cohort study in individuals aged 12 and older who received SARS-CoV-2 mRNA vaccination in British Columbia from December 15, 2020, to November 30, 2021. Exposure was defined as an ED visit or hospitalization for myocarditis within 21 days post-vaccination. The primary outcome was healthcare utilization, quantified as healthcare encounters in 12-month pre-index and post-index periods. Ratios of rate ratios (RRRs) for exposure-associated healthcare utilization were calculated using a difference-in-difference (DiD) analysis with a Poisson regression model.

Results: In the pre-index period, the exposed and unexposed groups showed minimal healthcare utilization rate difference (RD = 2.91 [95% CI, 2.29-3.52) compared to the substantial difference (RD = 12.76 [95% CI, 12.04-13.48) in the post-index period. DiD analysis revealed a 82% overall increase in healthcare utilization over 12 months among exposed individuals (RRR, 1.82 [95%CI, 1.25-2.66]). In the initial six months, healthcare utilization surpassed the 12-month estimate, exhibiting a 179% increase (RRR, 2.79 [95%CI, 1.80-4.33]), while the last 6 months showed no statistically significant change (RRR, 0.79 [95%CI, 0.49-1.29]). An additional 9.4 (95%CI, 8.9-10.1) visits per person were attributed to vaccine-associated myocarditis over 12 months (total excess = 936.2 healthcare visits).

Conclusions: Initial surge in healthcare visits among exposed, primarily comprised of outpatient follow-ups, highlighting thorough monitoring. Subsequent return to baseline rates suggests a favorable prognosis, indicating resolution of morbidity in vaccine-associated myocarditis, supporting the overall safety profile of the vaccine.