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

We evaluated all-cause healthcare utilization among those with vaccine-associated myocarditis, compared to vaccinees without postvaccination myocarditis.

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 postvaccination. 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.

In the postindex 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).

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