Objective This study aimed to identify cases of coronavirus disease 2019 (COVID-19) vaccine-associated subacute thyroiditis (SAT) during the active vaccination period of the pandemic, analyze the characteristics of these cases, and compare them with cases of non-vaccine associated SAT diagnosed in the same period. Methods A total of 55 patients diagnosed with SAT in our outpatient clinic between February and October, 2021, were included in this retrospective single-center study. Results Of the study population, 16 (29.1%) were diagnosed with COVID-19 vaccine-associated SAT (10 with CoronaVac® and six with Pfizer-BioNTech® vaccine), with a median time to onset of symptoms after vaccination of 6.5 (range, 2-20) days. There was no statistically significant difference between the vaccine-associated (VA) and non-vaccine associated (NVA) groups in terms of age, gender, time to diagnosis, thyroid volumes, thyroid function tests, and acute phase reactants. Seven (43.8%) and 25 (64.1%) patients were treated with methylprednisolone in the VA group and NVA group, respectively (p = 0.16). Follow-up data of 45 patients (16/16 for VA and 29/39 for NVA) were available. The mean follow-up of these patients was 47.4 ± 19.4 days, and the follow-up periods of the VA group and NVA group were comparable (p = 0.24). There was no difference between the two groups in terms of the frequency of euthyroidism at the follow-up visit (12/16 vs.14/29, p = 0.08). Conclusion With the increase in COVID-19 vaccination rates during the current pandemic, VA SAT cases are seen more frequently. The present study demonstrated that these cases have similar diagnostic features and clinical course to that of classic forms of SAT. In addition, most patients with VA SAT had a mild clinical course that improved with non-steroidal anti-inflammatory drugs.

Purpose An increasing number of cases of subacute thyroiditis (SAT) related to the coronavirus disease 2019 (COVID-19) and its vaccines continue to be published. The aim of this study was to investigate any change in the incidence and characteristics of SAT by comparing the pre-pandemic and pandemic periods. Methods This retrospective, single-center study included 432 newly-diagnosed SAT patients between January 2018 and December 2021. The annual frequency of SAT was calculated as the number of newly-diagnosed SAT cases divided by the total number of outpatients that year. Results The frequencies of newly-diagnosed SAT were 0.136% in 2018, 0.127% in 2019, 0.157% in 2020, and 0.114% in 2021 ( p = 0.19). While SAT patients were clustered in the autumn (35.1%) in 2018 and 2019, it was found that this cluster shifted to the winter (33.0%) in 2020 and 2021, in parallel with COVID-19 case peaks ( p = 0.017). The patients were separated into two groups as pre-COVID-19 pandemic SAT ( n = 272) and COVID-19 pandemic SAT ( n = 160). The mean ages of the groups were similar. There were more male patients in the COVID-19 pandemic SAT group than in the pre-pandemic group (30.6% vs. 18.7%, p = 0.005). Frequencies of overt hyperthyroidism and median free-thyroxine levels were significantly higher in the COVID-19 pandemic SAT group ( p = 0.029, p = 0.001). Treatment modalities, recurrence rates, and permanent hypothyroidism were similar in both groups. Conclusion With the COVID-19 pandemic, although there was a change in seasonal variation of SAT and an increase in the number of male patients, there was no change in the incidence and clinical course of SAT.

Background/Aim The aims of the study are to compare characteristics of subacute thyroiditis (SAT) related to different aetiologies, and to identify predictors of recurrence of SAT and incident hypothyroidism. Methods This nationwide multicenter retrospective cohort study included 53 endocrinology centers in Turkey. The study participants were divided into either coronavirus disease-2019 (COVID-19)-related SAT (Cov-SAT), severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccine-related SAT (Vac-SAT), or control SAT (Cont-SAT). Results Of the 811 patients, 258 (31·8%) were included in the Vac-SAT group, 98 (12·1%) in the Cov-SAT group, and 455 (56·1%) in the Cont-SAT group. No difference was found between the groups with regard to laboratory and imaging findings. The aetiology of SAT was not an independent predictor of recurrence or hypothyroidism. In the entire cohort, steroid therapy requirement and younger age were statistically significant predictors for SAT recurrence. C-reactive protein (CRP) measured during SAT onset, female gender, absence of anti-thyroid peroxidase (TPO) positivity, and absence of steroid therapy were statistically significant predictors of incident (early) hypothyroidism, irrespective of SAT aetiology. On the other hand, probable predictors of established hypothyroidism differed from that of incident hypothyroidism. Conclusion Since there is no difference in terms of follow-up parameters and outcomes, COVID-19- and SARS-CoV-2- vaccine related SATs can be treated and followed up like classical SATs. The recurrence was determined by the younger age and steroid therapy requirement. Steroid therapy independently predict incident hypothyroidism that may sometimes be transient in overall SATs and is also associated with lower risk of established hypothyroidism.