Effect of COVID-19 infection on thyroid function status and clinical indexes among hypothyroid outpatients

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spread rapidly, leading to an Omicron outbreak in Shanghai in mid-December after adjustments to the Coronavirus Disease 2019 (COVID-19) control strategy. To investigate the impact of COVID-19 infection among hypothyroid patients, we gathered data on the hypothyroid outpatients with COVID-19 infection during this time at the Thyroid Disease Center (TDC) of Shanghai Central Hospital. Patients were divided into two groups based on whether their hypothyroidism was caused by Hashimoto's Thyroiditis (HT): the HT and the non-HT group. We assessed the differences between pre-infection and clinical follow-up at one month (day (D) 30) and three months (D90) after COVID-19 infection. In HT group, thyroid-stimulating hormone (TSH) levels decreased significantly compared to pre-infection levels (<i>p</i> = 0.013), while free triiodothyronine (FT3) levels increased at D90 compared to both D30 post-infection and pre-infection levels (<i>p</i> < 0.001 and <i>p</i> = 0.005). Hemoglobin levels also increased after COVID-19 infection (<i>p</i> = 0.033). For non-HT patients, FT3 levels increased at D30 compared to pre-infection levels (<i>p</i> = 0.017). Moreover, inactivated SARS-CoV-2 vaccination can preserve thyroid function stability in patients with hypothyroidism.