Subacute Thyroiditis Developing Within 2 Days of Vaccination Against COVID-19 with BNT162b2 mRNA

A 32-year-old woman presented to the outpatient clinic with persistent fever, anterior neck pain, and palpitations over the past week which developed 2 days after she had received the first dose of the Pfizer/BioNTech SARS-CoV-2 mRNA vaccine. On examination, the patient’s heart rate was 140 beats per minute and the thyroid gland was tender on palpation. Laboratory studies showed a low serum TSH level with elevated free thyroxine. Thyroid ultrasound revealed low-echoic lesions compatible with the site of tenderness. The patient was diagnosed with subacute thyroiditis and treatment was initiated with acetaminophen and propranolol, which resulted in symptom resolution within 2 weeks. Clinicians should be aware that subacute thyroiditis may occur within a few days following COVID-19 vaccination, especially in patients with anterior cervical pain with no significant abnormal pharyngeal findings and/or severe palpitations, because differentiating them from early non-specific adverse reactions can be challenging. LEARNING POINTS: Cases of subacute thyroiditis after vaccination, including against COVID-19, have been increasingly reported. Subacute thyroiditis should be considered in patients with anterior cervical pain with no significant abnormal pharyngeal findings and/or severe palpitations after COVID-19 vaccination because these can be diagnostic clues. It is important to note that this condition can occur as early as a few days after vaccination, in order to avoid diagnostic pitfalls.