ASIA syndrome (autoimmune/inflammatory syndrome caused by adjuvants) is a postvaccination condition that develops after exposure to adjuvants in vaccinations that enhance immune responses. There is relatively little evidence on ASIA syndrome after severe acute respiratory syndrome coronavirus 2 vaccinations. The purpose of this study is to describe instances of subacute thyroiditis caused by the SARS-CoV-2 vaccination. The clinical, biochemical, and imaging characteristics of three instances of subacute thyroiditis following inactivated SARS-CoV-2 vaccination are described. Three female healthcare workers presented to our clinic four to seven days after receiving SARS-CoV-2 immunisation, complaining of anterior neck discomfort and tiredness. Two of them were in the process of nursing. There was no history of thyroid illness, upper respiratory tract infection, or COVID-19, and they tested negative for thyroid antibodies. The results of the laboratory tests and imaging were compatible with subacute thyroiditis. As part of the ASIA syndrome, SARS-CoV-2 immunisation can cause subacute thyroiditis. Subacute thyroiditis can occur within a few days of receiving the SARS-CoV-2 vaccine. Being in the postpartum phase may have aided the development of ASIA syndrome following the SARS-CoV-2 vaccine. 

This is the first case of ASIA syndrome-related subacute thyroiditis following inactivated COVID-19 immunisation. Clinicians should be aware that after receiving the inactive SARS-CoV-2 vaccination, subacute thyroiditis may occur as a symptom of ASIA syndrome.