Three Cases of Subacute Thyroiditis Following SARS-CoV-2 Vaccine: Postvaccination ASIA Syndrome

Context Autoimmune/inflammatory syndrome induced by adjuvants (ASIA syndrome) can be seen as a postvaccination phenomenon that occurs after exposure to adjuvants in vaccines that increase the immune responses. There are very limited data regarding ASIA syndrome following severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccines. Objectives This work aims to report cases of subacute thyroiditis related to the SARS-CoV-2 vaccine. Methods We describe the clinical, laboratory, and imaging features of 3 cases of subacute thyroiditis after inactivated SARS-CoV-2 vaccine (CoronaVac®). Three female healthcare workers have applied to our clinic with anterior neck pain and fatigue 4 to 7 days after SARS-CoV-2 vaccination. Two of them were in the breastfeeding period. They were negative for thyroid antibodies, and there was no previous history of thyroid disease, upper respiratory tract infection, or COVID-19. Laboratory test results and imaging findings were consistent with subacute thyroiditis. Results SARS-CoV-2 vaccination can lead to subacute thyroiditis as a phenomenon of ASIA syndrome. Subacute thyroiditis may develop within a few days after the SARS-CoV-2 vaccination. Being in the postpartum period may be a facilitating factor for the development of ASIA syndrome after the SARS-CoV-2 vaccination. Conclusions This is the first report of subacute thyroiditis as a phenomenon of ASIA syndrome after inactivated COVID-19 vaccination. Clinicians should be aware that subacute thyroiditis may develop as a manifestation of ASIA syndrome after the inactive SARS-CoV-2 vaccine.