Safety of Inactivated and mRNA COVID-19 Vaccination Among Patients Treated for Hypothyroidism: A Population-Based Cohort Study.

ABSTRACT

Background: Thyroiditis and Graves' disease have been reported after coronavirus disease 2019 (COVID-19) vaccination. We evaluated the risks of adverse events after COVID-19 vaccination among patients treated for hypothyroidism. Methods: In this retrospective population-based cohort study of Hong Kong Hospital Authority electronic health records with the Department of Health vaccination records linkage, levothyroxine (LT4) users were categorized into unvaccinated, vaccinated with BNT162b2 (mRNA vaccine), or CoronaVac (inactivated vaccine) between February 23, 2021, and September 9, 2021. Study outcomes were dosage reduction or escalation in LT4, emergency department (ED) visit, unscheduled hospitalization, adverse events of special interest (AESI) according to the World Health Organization's Global Advisory Committee on Vaccine Safety, and all-cause mortality. Inverse probability of treatment weighting for propensity score was applied to balance baseline patient characteristics among the three groups. Hazard ratios (HR) were estimated using Cox regression models. Patients were observed from the index date until the occurrence of study outcome, death, or censored on September 30, 2021, whichever came first. Results: In total, 47,086 LT4 users were identified (BNT162b2 n = 12,310; CoronaVac n = 11,353; and unvaccinated n = 23,423). COVID-19 vaccination was not associated with increased risks of LT4 dosage reduction (BNT162b2 HR = 0.971 [confidence interval; CI 0.892-1.058]; CoronaVac HR = 0.968 [CI 0.904-1.037]) or escalation (BNT162b2 HR = 0.779 [CI 0.519-1.169]; CoronaVac HR = 0.715 [CI 0.481-1.062]). Besides, COVID-19 vaccination was not associated with a higher risk of ED visits (BNT162b2 HR = 0.944 [CI 0.700-1.273]; CoronaVac HR = 0.851 [CI 0.647-1.120]) or unscheduled hospitalization (BNT162b2 HR = 0.905 [CI 0.539-1.520]; CoronaVac HR = 0.735 [CI 0.448-1.207]). There were two (0.016%) deaths and six (0.062%) AESI recorded for BNT162b2 recipients, and one (0.009%) and three (0.035%) for CoronaVac recipients, respectively. Conclusions: BNT162b2 or CoronaVac vaccination is not associated with unstable thyroid status or an increased risk of adverse outcomes among patients treated for hypothyroidism in general. These reassuring data should encourage them to get vaccinated against COVID-19 for protection from potentially worse COVID-19-related outcomes.