Healthcare utilization among COVID-19 mRNA vaccine-associated myocarditis cases: a matched retrospective cohort study.

Objectives: We evaluated all-cause healthcare utilization among those with vaccine-associated myocarditis, compared to vaccinees without post-vaccination myocarditis.

Methods: We conducted a retrospective cohort study in individuals aged 12 and older who received COVID-19 mRNA vaccination in British Columbia. Exposure was defined as an ED visit or hospitalization for myocarditis within 21 days post-vaccination. The primary outcome was healthcare utilization. Ratios of rate ratios (RRRs) for exposure-associated healthcare utilization were calculated using a difference-in-differences (DiD) analysis.

Results: In the post-index period, the exposed and unexposed groups showed substantial utilization rate difference (RD = 15.30 [95% CI, 14.47-16.13). A 51% overall increase in healthcare utilization was observed over 18 months among exposed individuals (RRR, 1.51 [95%CI, 1.08-2.11]). In the initial six months, healthcare utilization surpassed the 18-month estimate, exhibiting a 125% increase (RRR, 2.25 [95%CI, 1.43-3.52]), while the last 12 months showed no statistically significant change (RRR, 1.03 [95%CI, 0.72-1.47]). An additional 9.1 (95%CI, 8.53-9.71) visits per person were attributed to vaccine-associated myocarditis over 18 months (total excess = 938.26 healthcare visits).

Conclusion: The initial surge in healthcare visits post-exposure, mainly outpatient follow-ups, followed by a return to baseline rates, indicates a positive prognosis and supports the vaccine's safety profile.