Impact of COVID-19 Vaccination on Thyroid Disorders in Over 7 Million Adults and 200,000 Adolescents

Overview

This large nationwide study of over 7.5 million adults and 241,000 adolescents in South Korea found no increased risk of most thyroid diseases following COVID-19 vaccination. However, an increased risk of hypothyroidism exacerbation was observed post-vaccination in adults, while risks for hyperthyroidism, subacute thyroiditis, and thyroid eye disease were not significantly elevated.

Background

COVID-19 vaccines have been critical in reducing morbidity and mortality during the pandemic. Despite their benefits, concerns have emerged about potential associations between vaccination and thyroid dysfunction, particularly thyroiditis. Prior evidence mainly consists of case reports and small series, which do not quantify risk. This study uses a nationwide cohort and a self-controlled case series design to assess the incidence of new-onset and exacerbated thyroid diseases following COVID-19 vaccination across diverse populations including adolescents.

Data Highlights

Key Findings

• No significant increase in risk of hyperthyroidism following either first or second COVID-19 vaccine dose in adults.
• Observed increased risk of hypothyroidism exacerbation after vaccination, particularly after the first dose.
• No statistically significant increased risk of subacute thyroiditis post-vaccination, though point estimates were slightly elevated.
• Thyroid eye disease risk was not increased after vaccination; in fact, a decreased risk was noted after the first dose.
• Subgroup analyses by age, sex, and vaccine type showed no significant differences in thyroid disease incidence.
• In adolescents aged 12 to 17 years, no increased risk of thyroid diseases was observed after vaccination.

Clinical Implications

Clinicians can reassure patients that COVID-19 vaccination does not increase the risk of most thyroid disorders, including hyperthyroidism and subacute thyroiditis. However, patients with preexisting hypothyroidism should be monitored for potential exacerbation following vaccination. Overall, these findings support the safety of COVID-19 vaccines in relation to thyroid health across age groups.

Conclusion

This extensive nationwide study confirms that COVID-19 vaccination is not associated with increased risk of most thyroid diseases, though hypothyroidism exacerbation may occur. These results reinforce the favorable safety profile of COVID-19 vaccines regarding thyroid function.

References

1. Korea Disease Control and Prevention Agency-COVID-19-National Health Insurance Service cohort