In Sheffield we encountered a case of subacute thyroiditis occurring after COVID-19 vaccination. We therefore conducted an email survey through the Society for Endocrinology asking members to report subacute thyroiditis occurring in individuals within 28 days of administration of a COVID-19 vaccine. Eighteen cases fulfilling these criteria were detailed in survey responses. Eight were from the UK, 15 reports were received from doctors and 3 were from patients. Eleven of the cases followed Pfizer-BioNTech mRNA vaccination, six followed AZ ChAdOx1 S [recombinant] vaccination and one occurred after Moderna mRNA vaccination. Ten cases of thyroiditis developed after a first dose of vaccine and eight after a second dose. Cases presented a mean of 14.8 days after vaccination (range 1-28). On presentation the median fT4 was 1.38 times upper limit of normal (31.7 pmol/L) with results from normal up to >100 pmol/L (n=13; RR 12-22). The median C reactive protein (CRP) was 66.5 mg/L (RR 0-5, n=10) and the median erythrocyte sedimentation rate (ESR) 55 mm/hr (RR 1-15, n=8). Individual case details, where provided, ranged from mild self-limiting disease to those with severe symptoms requiring glucocorticoid treatment.

Discussion
A significant number of cases were reported in this survey where there was a temporal association between COVID-19 vaccination and the onset of subacute thyroiditis. It appears likely that COVID-19 vaccines triggered subacute thyroiditis in these cases due to an autoimmune/inflammatory (ASIA) syndrome induced by the vaccine adjuvants. These adjuvants bolster immune responses and protect the vaccines. Case reports and small case series of subacute thyroiditis following COVID-19 vaccination have recently been described.

Endocrinologists need be aware of potential vaccine sequalae when managing thyrotoxic patients, including the heightened risk that thyrotoxicosis following COVID-19 vaccination will result from a potentially self-limiting subacute thyroiditis. It has also been reported that Graves’ disease can develop in this situation. With over 1 billion COVID-19 vaccine doses administered to date, and a background subacute thyroiditis incidence of 4.9 per 100,000, there remains a caveat that these cases reported by Society members may have arisen by chance.

Authors:

William M Bennet

Aisha Elamin

John D Newell-Price