Abstract
Objectives
We evaluated impact of COVID-19 vaccination on thyroid function and antibodies, and influence of pre-existing thyroid autoimmunity on neutralizing antibody (NAb) responses.
Methods
Adults without history of COVID-19/thyroid disorders who received COVID-19 vaccination during June–August 2021 were recruited. All received two doses of vaccines. Thyroid-stimulating hormone (TSH), free thyroxine (fT4), free triiodothyronine (fT3), anti-thyroid peroxidase (anti-TPO) and anti-thyroglobulin (anti-Tg) antibodies were measured at baseline and 8 weeks post-vaccination. NAb against SARS-CoV-2 receptor-binding domain was measured.
Results
215 individuals were included (129[60%] BNT162b2; 86[40%] CoronaVac recipients): mean age 49.6 years, 37.2% men, and 12.1% anti-TPO/Tg positive at baseline. After vaccination, TSH did not change (p=0.225), but fT4 slightly increased (from 12.0±1.1 to 12.2±1.2pmol/L [from 0.93±0.09 to 0.95±0.09ng/dL], p<0.001) and fT3 slightly decreased (from 4.1±0.4 to 4.0±0.4pmol/L [from 2.67±0.26 to 2.60±0.26pg/mL], p<0.001). Only 3 patients (1.4%) had abnormal thyroid function post-vaccination, none clinically overt. Anti-TPO and anti-Tg titres increased modestly after vaccination (p<0.001), without significant changes in anti-TPO/Tg positivity. Changes in thyroid function and anti-thyroid antibodies were consistent between BNT162b2 and CoronaVac recipients, except for greater anti-TPO titre rise post-BNT162b2 (p<0.001). NAb responses were similar between individuals with and without pre-existing thyroid autoimmunity (p=0.855).
Conclusion
COVID-19 vaccination was associated with modest increase in anti-thyroid antibody titres. Anti-TPO increase was greater among BNT162b2 recipients. However, there was no clinically significant thyroid dysfunction post-vaccination. NAb responses were not influenced by pre-existing thyroid autoimmunity. Our results provided important reassurance for people to receive COVID-19 vaccination.
Keywords: COVID-19, SARS-CoV-2, vaccines, thyroid function tests, autoimmunity