Subacute Thyroiditis After mRNA Vaccine for Covid-19

Introduction: Subacute thyroiditis is a well-documented clinical condition which typically presents 1-2 weeks after an acute viral illness. Presenting symptoms are classically those of thyrotoxicosis but with associated tenderness in the thyroid. Treatment of acute symptoms is possible and the thyroid function will generally normalize with time. Subacute thyroiditis has rarely been reported after administration of viral vaccinations such as the seasonal flu vaccine. We present a case of subacute thyroiditis which presented after administration of the mRNA COVID-19 vaccine. Case: Patient is a 42yo female with no past medical history. She received the first dose of the Pfizer/BioNTech mRNA vaccine for COVID-19 on 12/22/20. Five days later, the patient complained of sore throat and palpitations. These symptoms progressed and she was evaluated in an urgent care on 12/31/20 where she was found to have tachycardia. Infectious work-up, including PCR for COVID-19, was negative and she was sent home. She took ibuprofen with some improvement of her symptoms. The following day she went to the ED; she was found to have a heart rate in the 130s with sinus tachycardia on EKG. Thyroid function testing was done which revealed TSH <0.01, fT4 4.58, fT3 11.8. Her TPO antibody was <28 and inflammatory markers were elevated including sed rate of 62. The patient was prescribed prednisone 40mg daily and propranolol 20mg as needed for symptoms. She reports rapid improvement of symptoms with prednisone. On 1/21/20, thyroid function showed TSH <0.01, fT4 down to 3.2, tT3 normal at 135. Thyroglobulin was elevated at 140.8 with negative thyroglobulin antibody, TRAb and TSI. Her inflammatory markers had decreased with sed rate of 26 and normal C-reactive protein. She had improved symptoms. Discussion: Cases of subacute thyroiditis are most commonly associated with upper respiratory viruses but cases have been reported with traditional inactivated viral vaccines or live-attenuated vaccines such as those for annual influenza. We present the case of a 42-year-old female who has presented with a classic case of subacute thyroiditis which occurred in the time frame after receiving the Pfizer mRNA vaccine for COVID-19. Research has been ongoing for decades regarding development of mRNA vaccines but the mRNA vaccines for the SARS-CoV-2 virus have been the first to be widely distributed to the general population. Thyroiditis has not been reported as a common side effect but the cross recognition between the coronavirus spike protein targeted with the mRNA vaccine and healthy thyroid cell antigens exists as evidenced by this case. Sources: 1. Prummel M, Strieder T, Wiersinga WM. The environment and autoimmune thyroid diseases. Eur J Endocrinol. 2004;150:605-618. Altay FA, Guz G, Altay M. 2. Subacute thyroiditis following seasonal influenza vaccination. Hum Vaccin Immunother. 2016;12(4):1033-1034.