hashimoto disease; Hypothyroidism; Arm pain; she is not immunocompromised and not sure why she received 3th dose; Headache; Fever; Chills; This spontaneous case was reported by a consumer and describes the occurrence of AUTOIMMUNE THYROIDITIS (hashimoto disease) and HYPOTHYROIDISM (Hypothyroidism) in a 35-year-old female patient who received mRNA-1273 (Moderna COVID-19 Vaccine) (batch no. 037C21A) for COVID-19 vaccination. The occurrence of additional non-serious events is detailed below.     Concurrent medical conditions included Hypothyroidism. Concomitant products included LEVOTHYROXINE SODIUM (SYNTHROID) and PARACETAMOL (TYLENOL) for an unknown indication.    On 18-Oct-2021, the patient received third dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) 1 dosage form. On an unknown date, the patient experienced AUTOIMMUNE THYROIDITIS (hashimoto disease) (seriousness criterion medically significant), HYPOTHYROIDISM (Hypothyroidism) (seriousness criterion medically significant), PAIN IN EXTREMITY (Arm pain), OFF LABEL USE (she is not immunocompromised and not sure why she received 3th dose), HEADACHE (Headache), PYREXIA (Fever) and CHILLS (Chills). At the time of the report, AUTOIMMUNE THYROIDITIS (hashimoto disease), HYPOTHYROIDISM (Hypothyroidism), PAIN IN EXTREMITY (Arm pain), HEADACHE (Headache), PYREXIA (Fever) and CHILLS (Chills) outcome was unknown and OFF LABEL USE (she is not immunocompromised and not sure why she received 3th dose) had resolved.        For mRNA-1273 (Moderna COVID-19 Vaccine) (Unknown), the reporter did not provide any causality assessments.   Concomitant medications include Synthroid and Tylenol.  Caller says she was not immunocompromised and not sure why she received 3th dose. patient reports having Hypothyroidism. No allergy was reported.  Company Comment : This case concerns a 35-year-old female patient with d medical history of hypothyroidism who experienced the unexpected events of autoimmune thyroiditis and hypothyroidism. The events occurred following an unknown date after the third dose of mRNA-1273 (Moderna COVID-19 Vaccine).  The rechallenge was unknown as details pertaining to first and second doses were not disclosed. Causality assessment with product use was not provided by the reporter.  The benefit-risk relationship of mRNA-1273 vaccine is not affected by this report.  The event was assessed as serious per regulatory authority reporting.   Events are confounded by the patient's underlying history of hypothyroidism.; Sender's Comments: This case concerns a 35-year-old female patient with d medical history of hypothyroidism who experienced the unexpected events of autoimmune thyroiditis and hypothyroidism. The events occurred following an unknown date after the third dose of mRNA-1273 (Moderna COVID-19 Vaccine).  The rechallenge was unknown as details pertaining to first and second doses were not disclosed. Causality assessment with product use was not provided by the reporter.  The benefit-risk relationship of mRNA-1273 vaccine is not affected by this report.  The event was assessed as serious per regulatory authority reporting.   Events are confounded by the patient's underlying history of hypothyroidism.