The role of COVID-19 infection and vaccination in the induction of anti-TPO antibodies and the potential impact on developing thyroid disease

COVID-19 infection and/or vaccination has been repeatedly reported to be the cause of initiating thyroid disease. Limited studies explored the impact of COVID-19 infection and/or vaccination on patients with thyroiditis history. This study aimed to relate COVID-19 infection and vaccination to the development of anti-Thyroid Peroxidase (TPO) auto-antibodies in groups of participants naturally infected with and/or vaccinated for COVID-19, with or without prior history of thyroid disease. Participants were grouped into infected only (n = 75), vaccinated only (n = 122), infected and vaccinated (n = 97), infected/vaccinated with prior thyroid disease (n = 35), children (n = 69) and pre-COVID controls (n = 146). Participants were screened for anti-Spike and anti-Nucleocapsid, and anti- TPO antibodies. Anti-TPO positive participants were tested for thyroid function by measuring TSH, free T3 and free T4. Significantly highest anti-TPO titers (mean = 91.45 IU/mL) and seropositivity rates (42.49%) were found in participants with pre-established thyroid disease. Combined infected and vaccinated participants with no history of thyroid disease also showed significantly higher anti-TPO titers (mean = 74.22 IU/mL, 17.5%) compared to vaccinated only (mean = 48.04 IU/mL, 15.6%), infected only (mean = 31.54 IU/mL, 12%), and control pediatric (mean = 4.8 IU/mL, 1.4%) and pre-COVID (mean = 20.16 IU/mL, 11%) groups. Among anti-TPO positive participants, TSH levels positively correlated with anti-TPO titers. Anti-TPO titers were significantly affected by number of vaccine doses but not with anti-Spike titers, anti-Nucleocapsid titers, number of COVID-19 infections or vaccine types. Age formed a significant factor correlating positively with mean anti-TPO titers. Elevated anti-TPO titers appeared more frequently months after infection and/or vaccination. With accumulation of COVID-19 related immune events, patients with pre-established thyroid disease showed higher anti-TPO titers compared to those with no history of thyroid disease. This indicates that such immune events might boost the activation of pre-existing TPO specific T and B cells. Clinical follow up of thyroiditis patients during and months after COVID-19 infection/vaccination is essential.