The effect of COVID-19 vaccines on thyroid function and thyroid autoimmunity

Aims: There have been reports about various thyroid autoimmune events after SARS-CoV-2 vaccinations. There is limited data on the extent to which vaccines for COVID-19 are effective on thyroid autoimmunity. This study investigates how COVID-19 vaccination affects thyroid antibodies and functions in individuals without any thyroid disease history. Methods: The study evaluated individuals aged 18-65 with no previous COVID-19 history or thyroid disease who had at least two COVID-19 vaccine doses (CoronaVac + Pfizer-BioNTech or Pfizer-BioNTech alone) between October 2021 and October 2022. All participants' thyroid hormone (free triiodothyronine, thyroid-stimulating hormone, and free thyroxine) and thyroid autoantibody (anti-thyroglobulin, antithyroid peroxidase, and TSH receptor antibody) levels were measured. Results: The study included 92 individuals in total. Thyroid functions and antithyroid antibody levels were found to be in the normal range before the implementation of the SARS-CoV-2 vaccine. Of the study participants, 42 received the Sinovac + BioNTech vaccine, and 50 received the BioNTech vaccine alone. While a decrease in st4 value was observed only in the BioNTech group after vaccination (p=0.007), thyroid dysfunction was not observed in any participant. After vaccination, TRAB positivity was observed in one participant, ANTI-TPO positivity in six participants, and ANTI-TG positivity in eight participants. No statistically significant antibody positivity was detected. No participants with antibody positivity displayed thyroid dysfunction. Conclusion: Although some positivity in terms of antithyroid antibodies was observed after COVID-19 vaccination, this antibody positivity did not have a statistically significant level, and thyroid dysfunction was not detected in any participant. The COVID-19 vaccine is safe for thyroid function and autoimmunity.