Thyrotoxicosis after COVID-19 vaccination.

Dear Editor,

We would like to share ideas on the publication “Thyrotoxicosis after COVID-19 vaccination: seven case reports and a literature review” [1]. Lee et al. concluded that “COVID-19 vaccines can cause not only destructive thyroiditis but also AIT… relationship between COVID-19, vaccines, and thyroid diseases” [1]. We agree that the post-COVID-19 vaccination thyroid problem might occur and there might be an association with pathological/abnormal immune response to vaccine. In the present study, a change of thyroxine level is well demonstrated and there is a trend of decreasing when time passes. After vaccination, there is also another important process that might contribute to thyrotoxicosis occurrence. The vaccine can induce increased blood viscosity [2]. The association between hyperviscosity and thyrotoxicosis is proposed [3]. An increasing of blood viscosity is due to rapid increased level of antibody after vaccination and the viscosity will decrease when there is a decline of antibody level. This pattern is the same as observed alteration of thyroid hormone level in the present report by Lee et al. [1]. Finally, if thyroid hormone test is based on immunoassay, an interference, a false aberration of hormone level might be induced by a high blood viscosity [4].