Subacute thyroiditis and COVID-19 vaccines: a case/non-case study

Some case reports have suggested a possible association between COVID-19 vaccines and subacute thyroiditis (SAT), however, to our knowledge, no study has analyzed this possible relationship. This study aimed to analyze whether a disproportionate number of cases of SAT were reported in the EudraVigilance database for four COVID-19 vaccines (BNT162b2, mRNA-1273 ChAdOx1-S or Ad26.COV2.S).

A case/non-case study was conducted to assess the association between SAT and COVID-19 vaccines, calculating the reporting odds ratios (RORs) up to December 2, 2021. Cases were selected using the preferred term 'subacute thyroiditis'. First, cases involving COVID-19 vaccines were compared with those involving all other drugs. Secondly, the RORs for COVID-19 vaccines compared with other viral vaccines (overall and influenza vaccines only) were obtained.

Until December 2, 2021, of 1,221,582 spontaneous cases of adverse reactions with the four vaccines, we found 162 SAT cases: BNT162b2 (n = 103), mRNA-1273 (n = 27), ChAdOx1-S (n = 31) and Ad26.COV2.S (n = 1). SAT cases were found to be reported more frequently in association with BNT162b2, mRNA-1273, and ChAdOx1-S vaccines than with other drugs. Moreover, we found a signal of disproportionate reporting for SAT with BNT162b2 and mRNA-1273 vaccines comparing with other viral vaccines (BNT162b2 ROR 3.58, 95% CI 1.92-6.66; mRNA-1273 ROR 3.44, 95% CI 1.71-6.94). However, this association was absent when these COVID-19 vaccines were compared with influenza vaccines.

In EudraVigilance, SAT is relatively more frequently reported in association with mRNA COVID-19 vaccines than with other viral vaccines. Well designed observational studies are needed to confirm these results.