Cohorts were defined using Providence St Joseph Health electronic health records, which include imported state vaccination records. Unvaccinated (no COVID-19 vaccines received), COVID-19 mRNA vaccinated (two-dose vaccination with mRNA-1273 or BNT162b2 PfizerBioNTech), and boosted (three doses of mRNA-1273 or BNT162b2 PfizerBioNTech) cohorts were defined. In addition, the vaccinated unboosted cohort was defined as people who were vaccinated (two-dose vaccination with mRNA-1273 or BNT162b2 PfizerBioNTech, delivered after boosters became available in the USA (on Sept 22, 2021), and were eligible for a booster (6 months after second dose). Finally, propensity score matching was used to control for common covariates to generate the unvaccinated matched and the vaccinated unboosted matched cohorts.
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