A case of subacute thyroiditis after influenza vaccination.

After influenza vaccination, subacute thyroiditis (SAT) may develop. If persistent fever, anterior neck pain, swelling, tenderness of the thyroid gland, and symptoms of thyrotoxicosis are observed immediately after vaccination for several viruses, including influenza, an examination to rule out the onset of SAT is recommended. Human leukocyte antigen type A2 (HLA-A2) and HLA-B35 may be linked to the development of SAT following influenza vaccination. The two doses of the coronavirus disease 2019 (COVID-19) vaccine given before the influenza vaccine may affect the onset of SAT.