Retrospective Observation of Subacute Thyroiditis Before and During the COVID-19 Vaccination Campaign in a Single Secondary Endocrine Centre in the Savona District, Liguria, Italy

Background Clinicians should be aware that subacute thyroiditis (SAT) might be an under-reported adverse effect of COVID-19 vaccines. Aim In records from endocrinological examinations, we reviewed the incidence of diagnoses of SAT from 2000 to 2020 and during the 2021 COVID-19 vaccination campaign. Methods Review of electronic records from June to December in each year from 2000 to 2021. Results From 2000 to 2020, 51 patients in our centre had SAT (0.6%). From June to December 2021, 7 females were diagnosed with SAT after vaccination. The percentage of SAT in 2021 medical files was 1.5%. SAT diagnoses significantly (P = 0.03) increased in 2021 in comparison with the 2000–2020 period. The median age of SAT patients in 2021 (51 years; IQR 35–66 years) was higher than in the 2000–2020 period (45 years, IQR 38–52 years; P = 0.05). Conclusion To date, few cases of SAT after COVID-19 vaccinations have been described in the literature, with sub-clinical, normal or increased thyroid function during 1-3-month follow-up. Our findings indicate that SAT after COVID-19 vaccination occurs more frequently than in other virus-related cases and at a greater age. Our observation of a local increase in SAT during the 2021 COVID-19 vaccination campaign indicates that physicians should be aware of this infrequent side effect, which must be considered and monitored after COVID-19 vaccination.