Effect of inactivated and mRNA COVID-19 vaccination on thyroid function among patients treated for hyperthyroidism.

OBJECTIVE
Among patients treated for hyperthyroidism, we evaluated factors associated with not receiving COVID-19 vaccination and whether COVID-19 vaccination was associated with thyroid function instability.


METHODS
We included consecutive patients treated for hyperthyroidism attending the Thyroid Clinic of a teaching hospital between January and September 2021. They were categorised into vaccinated and unvaccinated groups. The index date was the date of first-dose vaccination for vaccinated group, and the first date of attendance in the inclusion period for unvaccinated group. They were followed up until March 2022 or occurrence of thyroid function instability (worsening of thyroid function/increase in anti-thyroid drug dosage), whichever was earlier.


RESULTS
910 patients were included (mean age 51.6 years; 82.1% female). 86.2% had Graves' disease. 67.3% were vaccinated (67.3% BNT162b2; 30.6% CoronaVac; 2.1% heterologous). Abnormal thyroid function and cardiovascular comorbidities were independently associated with unvaccinated status. Upon median follow-up of 5.3 months, thyroid function instability occurred in 15.9% of patients. COVID-19 vaccination did not increase risks of thyroid function instability (HR 0.78, 95%CI 0.56-1.09, p = 0.151): consistent in Graves' disease, both types of vaccines, and regardless of whether baseline thyroid function was normal. Twenty-seven patients overtly thyrotoxic at the time of vaccination received COVID-19 vaccines without triggering thyroid storm or difficulty in subsequent thyroid function control.


CONCLUSION
Among patients treated for hyperthyroidism, abnormal thyroid function was a factor predicting unvaccinated status. Our results should encourage patients treated for hyperthyroidism to receive COVID-19 vaccination to protect themselves from adverse outcomes and potential long-term sequelae of COVID-19.