Gastritis; This symptom made the patient lose 22 pounds/Heavy weight loss up to 20 pounds/ Weight loss; Hyper acidity; Epstein-Barr virus aggravation; Thyroid gland was attacked/Thyroid glands were swollen; Swollen throat; Cough; Decreased appetite; Fever for a couple of days/ Mild fever; Hyperthyroidism; Pain did not allow the patient to eat/Not able to eat anything because it attack the thyroid gland/ Big time difficulty swallowing the food; Sore throat; Lots of weakness/Heavy weakness; Tachycardia; Severe pain in the mouth joint; Severe pain in jaws; This spontaneous case was reported by a consumer and describes the occurrence of WEIGHT DECREASED (This symptom made the patient lose 22 pounds/Heavy weight loss up to 20 pounds/ Weight loss), HYPERCHLORHYDRIA (Hyper acidity) and GASTRITIS (Gastritis) in a 46-year-old male patient who received mRNA-1273 (Moderna COVID-19 Vaccine) (batch nos. 043B21A and 018B21A) for COVID-19 vaccination. The occurrence of additional non-serious events is detailed below.     The patient's past medical history included Epstein-Barr virus infection. Concurrent medical conditions included Hypercholesterolemia. Concomitant products included ATORVASTATIN for Hypercholesterolemia, MINERALS NOS, VITAMINS NOS (VITAL [MINERALS NOS;VITAMINS NOS]) from 13-Sep-2019 to an unknown date and CYANOCOBALAMIN (VITAMIN B-12) from 13-Sep-2019 to an unknown date for Vitamin supplementation.   On 26-Mar-2021, the patient received first dose of mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular) 1 dosage form. On 23-Apr-2021, received second dose of mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular) dosage was changed to 1 dosage form. On 24-Apr-2021, the patient experienced ORAL PAIN (Severe pain in the mouth joint) and PAIN IN JAW (Severe pain in jaws). On 25-Apr-2021, the patient experienced WEIGHT DECREASED (This symptom made the patient lose 22 pounds/Heavy weight loss up to 20 pounds/ Weight loss) (seriousness criterion hospitalization), HYPERCHLORHYDRIA (Hyper acidity) (seriousness criterion hospitalization), HYPERTHYROIDISM (Hyperthyroidism), FEEDING DISORDER (Pain did not allow the patient to eat/Not able to eat anything because it attack the thyroid gland/ Big time difficulty swallowing the food), ASTHENIA (Lots of weakness/Heavy weakness), TACHYCARDIA (Tachycardia), COUGH (Cough) and DECREASED APPETITE (Decreased appetite). 25-Apr-2021, the patient experienced OROPHARYNGEAL PAIN (Sore throat). 25-Apr-2021, the patient experienced PYREXIA (Fever for a couple of days/ Mild fever). On 26-Apr-2021, the patient experienced PHARYNGEAL SWELLING (Swollen throat). On 06-May-2021, the patient experienced GOITRE (Thyroid gland was attacked/Thyroid glands were swollen). On 11-May-2021, the patient experienced EPSTEIN-BARR VIRUS INFECTION (Epstein-Barr virus aggravation). On an unknown date, the patient experienced GASTRITIS (Gastritis) (seriousness criterion hospitalization). The patient was hospitalized from 06-May-2021 to 16-May-2021 due to HYPERCHLORHYDRIA and WEIGHT DECREASED. The patient was treated with METHIMAZOLE on 14-May-2021 at a dose of 10 mg twice a day; OMEPRAZOLE on 14-May-2021 at a dose of 20 mg once a day and BENZONATATE on 14-May-2021 at a dose of 100 mg three times a day. On 06-May-2021, WEIGHT DECREASED (This symptom made the patient lose 22 pounds/Heavy weight loss up to 20 pounds/ Weight loss), PAIN IN JAW (Severe pain in jaws), OROPHARYNGEAL PAIN (Sore throat), PHARYNGEAL SWELLING (Swollen throat), COUGH (Cough) and PYREXIA (Fever for a couple of days/ Mild fever) had resolved. At the time of the report, HYPERCHLORHYDRIA (Hyper acidity), HYPERTHYROIDISM (Hyperthyroidism) and ORAL PAIN (Severe pain in the mouth joint) had resolved, GASTRITIS (Gastritis), TACHYCARDIA (Tachycardia) and EPSTEIN-BARR VIRUS INFECTION (Epstein-Barr virus aggravation) outcome was unknown and FEEDING DISORDER (Pain did not allow the patient to eat/Not able to eat anything because it attack the thyroid gland/ Big time difficulty swallowing the food), ASTHENIA (Lots of weakness/Heavy weakness), DECREASED APPETITE (Decreased appetite) and GOITRE (Thyroid gland was attacked/Thyroid glands were swollen) was resolving.      DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): On 06-May-2021, Endoscopy: abnormal (abnormal) Normal with having a minor gastritis; another observation was thyroid glands were swollen. On 07-May-2021, Blood test: abnormal (abnormal) Diagnosed with hyperthyroidism and EPSTEIN-BARR VIRUS aggravation.. On 16-May-2021, Blood test: normal (normal) Normal. On 17-May-2021, Blood test: normal (normal) Normal. On an unknown date, Blood test: normal (normal) Normal.         As per the physicians observations Epsein Barr virus aggravation which might have affected the thyroid glands and that E-B virus might have aggravated because of the hormonal or other changes which might have happened due to the COVID-19 / mRNA-1273 vaccination.  Company comment: Based on current available information and the temporal association between product use and the start date of the events a causal relationship cannot be excluded.   Most recent FOLLOW-UP information incorporated above includes: On 19-Aug-2021: Added relevant history, concomitant medication details, laboratory, added adverse event details, added seriousness criteria, investigation details, treatment medication details and additional information's.; Sender's Comments: Based on current available information and the temporal association between product use and the start date of the events a causal relationship cannot be excluded.