Thyroid Dysfunction Following SARS-CoV-2 Infection: Findings from a 12-Month Prospective Cohort Study

Introduction: SARS-CoV-2 infection has been increasingly associated with thyroid involvement, likely mediated by post-viral immune–inflammatory mechanisms. However, prospective data on the incidence and medium-term evolution of post-COVID thyroid dysfunction remain limited. Methods: We conducted a prospective, observational, single-center study including adult patients hospitalized for COVID-19 between December 2022 and December 2024. Thyroid function tests, thyroid autoantibodies, inflammatory markers, and thyroid ultrasound were assessed during hospitalization and re-evaluated at 4–6 weeks, 3, 6, and 12 months. Acute disease severity and administered treatments, including corticosteroid therapy, were recorded. Results: A total of 71 patients were enrolled, of whom 67 completed the 12-month follow-up. During follow-up, 6.0% of patients developed subacute thyroiditis and 11.9% developed autoimmune thyroiditis, with most cases showing a mild or self-limited clinical course. Persistence of thyroid autoantibodies at 12 months was observed in a subset of patients. Longitudinal assessment of thyroid hormones revealed an overall trend toward gradual normalization, with marked interindividual variability. Associations between thyroid dysfunction, systemic inflammation, and acute COVID-19 severity were weak. Conclusions: Post-COVID thyroid dysfunction, particularly subacute and autoimmune thyroiditis, was relatively frequent within the first 12 months after SARS-CoV-2 infection, even following mild or moderate acute disease. These findings support the need for risk-adapted thyroid monitoring in the post-COVID period and suggest a triggering role of SARS-CoV-2 for both transient thyroid dysfunction and persistent autoimmune processes.