Long-Term Thyroid Outcomes After COVID-19 Vaccination: A Cohort Study of 2 333 496 Patients From the TriNetX Network

<jats:title>Abstract</jats:title>
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<jats:title>Context</jats:title>
<jats:p>Reports on long-term thyroid dysfunction following COVID-19 vaccination are limited. Understanding the risk of subacute thyroiditis, hyperthyroidism, and hypothyroidism in vaccinated individuals is crucial for postvaccination monitoring.</jats:p>
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<jats:title>Objective</jats:title>
<jats:p>This study evaluated the risk of thyroid dysfunction in individuals vaccinated against COVID-19 compared to unvaccinated individuals, using a large cohort.</jats:p>
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<jats:title>Methods</jats:title>
<jats:p>We conducted a retrospective cohort study from January 1, 2022, to December 31, 2023, using the TriNetX database, including 1 166 748 vaccinated and 1 166 748 unvaccinated individuals. Propensity score matching was used to balance baseline characteristics. The primary outcomes were new diagnoses of subacute thyroiditis, hyperthyroidism, and hypothyroidism.</jats:p>
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<jats:title>Results</jats:title>
<jats:p>The risk of subacute thyroiditis remained unchanged (95% CIs included 1). A significant reduction in hyperthyroidism risk was observed from 3 to 9 months postvaccination (hazard ratios [HRs]: 0.65-0.89, all 95% CIs below 1), but this trend was not significant at 12 months (HR: 0.99; 95% CI: 0.92-1.06). In contrast, the risk of hypothyroidism significantly increased from 6 to 12 months postvaccination (HR: 1.14-1.30, all 95% CIs above 1). Among mRNA vaccine recipients, the risk of both hyperthyroidism and hypothyroidism was significantly elevated at 12 months (HR: 1.16-2.13).</jats:p>
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<jats:title>Conclusion</jats:title>
<jats:p>COVID-19 vaccination was associated with a reduced risk of hyperthyroidism and an increased risk of hypothyroidism, highlighting the need for ongoing thyroid function monitoring.</jats:p>
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