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.