The patient will now be using a wheelchair because when the tremors are in his legs the patient cannot walk.; continuing to experience tremors in all 4 extremities,; Tremors, only on the right arm; Tremors, only on the right arm; Tremors again in both arms; Patient started to experienced tremors, first on the left arm, and then on the right arm; This spontaneous case was reported by a consumer and describes the occurrence of GAIT DISTURBANCE (The patient will now be using a wheelchair because when the tremors are in his legs the patient cannot walk.) and TREMOR (continuing to experience tremors in all 4 extremities,) in a 21-year-old male patient who received mRNA-1273 (Moderna COVID-19 Vaccine) (batch nos. 051C21A and 050C21A) for COVID-19 vaccination. The occurrence of additional non-serious events is detailed below.     Concurrent medical conditions included Allergy NOS. Concomitant products included DIPHENHYDRAMINE HYDROCHLORIDE (BENADRYL [DIPHENHYDRAMINE HYDROCHLORIDE]) for Allergy NOS, MONTELUKAST SODIUM (SINGULAIR), SALBUTAMOL (VENTOLIN [SALBUTAMOL]), FLUTICASONE PROPIONATE (FLOVENT) and MONTELUKAST for an unknown indication.   On 26-May-2021, the patient received first dose of mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular) 1 dosage form. On 23-Jun-2021, received second dose of mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular) dosage was changed to 1 dosage form. On 23-Jun-2021,  after starting mRNA-1273 (Moderna COVID-19 Vaccine), the patient experienced TREMOR (Patient started to experienced tremors, first on the left arm, and then on the right arm). On 28-Jun-2021, the patient experienced TREMOR (Tremors again in both arms). On 02-Jul-2021, the patient experienced the first episode of TREMOR (Tremors, only on the right arm). On 04-Jul-2021, the patient experienced the second episode of TREMOR (Tremors, only on the right arm). On 05-Jul-2021, the patient experienced TREMOR (continuing to experience tremors in all 4 extremities,) (seriousness criterion disability). On an unknown date, the patient experienced GAIT DISTURBANCE (The patient will now be using a wheelchair because when the tremors are in his legs the patient cannot walk.) (seriousness criterion disability). The patient was treated with SALINE [SODIUM CHLORIDE] (intravenous) on 28-Jun-2021 at a dose of 1.5 liter and IBUPROFEN (MOTRIN [IBUPROFEN]) at an unspecified dose and frequency. On 23-Jun-2021, TREMOR (Patient started to experienced tremors, first on the left arm, and then on the right arm) had resolved. On 28-Jun-2021, TREMOR (Tremors again in both arms) had resolved. On 04-Jul-2021, last episode of TREMOR (Tremors, only on the right arm) had resolved. At the time of the report, GAIT DISTURBANCE (The patient will now be using a wheelchair because when the tremors are in his legs the patient cannot walk.) and TREMOR (continuing to experience tremors in all 4 extremities,) outcome was unknown.      DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): On 28-Jun-2021, Blood test: normal (normal) blood work came back normal..     For mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular), the reporter did not provide any causality assessments.   ER doctors thought patient may have been dehydrated, and ruled out Rhabdomyolysis with the blood work.  The patient went to see Neurologist on 13-Jul-2021.The patient was given a muscle relaxant that did not produce a beneficial result and underwent lab work, a basic neurological evaluation, and a CT scan.  Company comment: Based on the current available information and temporal association between the use of the product and the start date of the event, a causal relationship cannot be excluded. However, gait disturbance experienced by the patient is serious (disability) as tremors was not pre-existing prior to vaccine and gradually it worsened to an extent that he was unable to walk and was using wheel chair. Results of all diagnostics and current status is required for further assessment.   This case was linked to MOD-2021-246753 (Patient Link).   Most recent FOLLOW-UP information incorporated above includes: On 16-Jul-2021: Follow-up received on 16-Jul-2021 contains significant information: New event walking difficulty added, seriousness criteria medically significant added.; Sender's Comments: Based on the current available information and temporal association between the use of the product and the start date of the event, a causal relationship cannot be excluded. However, gait disturbance experienced by the patient is serious (disability) as tremors was not pre-existing prior to vaccine and gradually it worsened to an extent that he was unable to walk and was using wheel chair. Results of all diagnostics and current status is required for further assessment.