• WongCarlos King HoCKH0000-0002-6895-6071Centre for Safe Medication Practice and Research, Department of Pharmacology and Pharmacy, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China.Department of Family Medicine and Primary, David Tak Wai Lui, Xi Xiong, Celine Sze Ling Chui, Francisco Tsz Tsun Lai, Xue Li, Eric Yuk Fai Wan, Ching Lung Cheung, Chi Ho Lee, Yu Cho Woo, Ivan Chi Ho Au, Matthew Shing Hin Chung, Franco Wing Tak Cheng, TanKathryn Choon BengKCB0000-0001-9037-0416Department of Medicine, School of Clinical Medicine, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China., and WongIan Chi KeiICK0000-0001-8242-0014Centre for Safe Medication Practice and Research, Department of Pharmacology and Pharmacy, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China. wongick@hku.hk.Laboratory of Data Discovery.
• Centre for Safe Medication Practice and Research, Department of Pharmacology and Pharmacy, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China.
• Bmc Med. 2022 Oct 14; 20 (1): 339.

BackgroundIn view of accumulating case reports of thyroid dysfunction following COVID-19 vaccination, we evaluated the risks of incident thyroid dysfunction following inactivated (CoronaVac) and mRNA (BNT162b2) COVID-19 vaccines using a population-based dataset.MethodsWe identified people who received COVID-19 vaccination between 23 February and 30 September 2021 from a population-based electronic health database in Hong Kong, linked to vaccination records. Thyroid dysfunction encompassed anti-thyroid drug (ATD)/levothyroxine (LT4) initiation, biochemical picture of hyperthyroidism/hypothyroidism, incident Graves' disease (GD), and thyroiditis. A self-controlled case series design was used to estimate the incidence rate ratio (IRR) of thyroid dysfunction in a 56-day post-vaccination period compared to the baseline period (non-exposure period) using conditional Poisson regression.ResultsA total of 2,288,239 people received at least one dose of COVID-19 vaccination (57.8% BNT162b2 recipients and 42.2% CoronaVac recipients). 94.3% of BNT162b2 recipients and 92.2% of CoronaVac recipients received the second dose. Following the first dose of COVID-19 vaccination, there was no increase in the risks of ATD initiation (BNT162b2: IRR 0.864, 95% CI 0.670-1.114; CoronaVac: IRR 0.707, 95% CI 0.549-0.912), LT4 initiation (BNT162b2: IRR 0.911, 95% CI 0.716-1.159; CoronaVac: IRR 0.778, 95% CI 0.618-0.981), biochemical picture of hyperthyroidism (BNT162b2: IRR 0.872, 95% CI 0.744-1.023; CoronaVac: IRR 0.830, 95% CI 0.713-0.967) or hypothyroidism (BNT162b2: IRR 1.002, 95% CI 0.838-1.199; CoronaVac: IRR 0.963, 95% CI 0.807-1.149), GD, and thyroiditis. Similarly, following the second dose of COVID-19 vaccination, there was no increase in the risks of ATD initiation (BNT162b2: IRR 0.972, 95% CI 0.770-1.227; CoronaVac: IRR 0.879, 95%CI 0.693-1.116), LT4 initiation (BNT162b2: IRR 1.019, 95% CI 0.833-1.246; CoronaVac: IRR 0.768, 95% CI 0.613-0.962), hyperthyroidism (BNT162b2: IRR 1.039, 95% CI 0.899-1.201; CoronaVac: IRR 0.911, 95% CI 0.786-1.055), hypothyroidism (BNT162b2: IRR 0.935, 95% CI 0.794-1.102; CoronaVac: IRR 0.945, 95% CI 0.799-1.119), GD, and thyroiditis. Age- and sex-specific subgroup and sensitivity analyses showed consistent neutral associations between thyroid dysfunction and both types of COVID-19 vaccines.ConclusionsOur population-based study showed no evidence of vaccine-related increase in incident hyperthyroidism or hypothyroidism with both BNT162b2 and CoronaVac.© 2022. The Author(s).

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