Subacute Thyroiditis following COVID-19 and COVID-19 vaccination.

Objective COVID-19 infection and immunizations have been implicated in developing a range of thyroid diseases, including subacute thyroiditis (SAT). This study aimed to evaluate the association between COVID-19 infection and/or COVID-19 vaccination with SAT. Methods A population of 3 million adults insured by Clalit Health Services (CHS) was evaluated from March 2020 to September 2022. Patients with a new diagnosis of SAT were identified and matched in a 1:10 ratio to a control group. Each control was assigned an index date that was identical to that of their matched case, defined as the date of SAT diagnosis. Multivariate conditional logistic regression models were used to evaluate the association between COVID-19 infection, vaccine, and thyroiditis. Results A total of 3,221 patients with SAT were matched with 32,210 controls. Rates of COVID-19 vaccination (first, second, or third dose) and COVID-19 infection were evaluated prior to the date of SAT diagnosis (disease group) or index date (control group) to detect a possible association. No difference was detected between the groups in relation to vaccinations at the 30 days, 60 days, and 90 days’time points (p=0.880/0.335/0.174 respectively). No difference was found between groups in relation to COVID-19 infection at these time points (p=0.735/0.362/0.956 respectively). There was higher use of medications for the treatment of thyroiditis, including NSAIDs (28.6% vs. 7.9%, p<0.01), steroids (10.3% vs. 1.8%, p<0.01), and beta-blockers (18.3% vs. 5.4%, p<0.01). Conclusion Based on this large population study, no association was found between COVID-19 infection and/or the COVID-19 vaccine and SAT.