never received hissecond Moderna vaccine; Arthritis in his 1st and 2nd digits of the hands, and not his 3rd-5th/reactive arthritis after first Moderna shot; Could not open or close hand or make a fist; This spontaneous case was reported by a physician and describes the occurrence of ARTHRITIS (Arthritis in his 1st and 2nd digits of the hands, and not his 3rd-5th/reactive arthritis after first Moderna shot), MOBILITY DECREASED (Could not open or close hand or make a fist) and PRODUCT DOSE OMISSION ISSUE (never received hissecond Moderna vaccine) in a 73-year-old male patient who received mRNA-1273 (Moderna COVID-19 Vaccine) for COVID-19 vaccination.     No Medical History information was reported.    In December 2020, the patient received first dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) 1 dosage form. In December 2020, the patient experienced ARTHRITIS (Arthritis in his 1st and 2nd digits of the hands, and not his 3rd-5th/reactive arthritis after first Moderna shot) and MOBILITY DECREASED (Could not open or close hand or make a fist). On an unknown date, the patient experienced PRODUCT DOSE OMISSION ISSUE (never received hissecond Moderna vaccine). The patient was treated with PREDNISONE for Hand arthritis, at a dose of 40 mg for 4 days then tapered for 3 and PREDNISONE for Hand arthritis, at a dose of : 40 mg for 4 days then tapered for 3. At the time of the report, ARTHRITIS (Arthritis in his 1st and 2nd digits of the hands, and not his 3rd-5th/reactive arthritis after first Moderna shot) was resolving, MOBILITY DECREASED (Could not open or close hand or make a fist) outcome was unknown and PRODUCT DOSE OMISSION ISSUE (never received hissecond Moderna vaccine) had resolved.      DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): In January 2021, Nucleic acid test: negative (Negative) probably did not have the COVID-19 virus in Jan2021. On 28-Jan-2021, Antibody test: positive (Positive) had antibodies present. In May 2021, Antibody test: positive (Positive) Have the spike protein on antibody testing in May 2021.. On 28-May-2021, Antibody test: positive (Positive) had antibodies present.     mRNA-1273 (Moderna COVID-19 Vaccine) (Unknown) was withdrawn on an unknown date.   For mRNA-1273 (Moderna COVID-19 Vaccine) (Unknown), the reporter did not provide any causality assessments.   No concomitant medications were reported.   The reactive arthritis had resolved by 95-97 percent.   Most recent FOLLOW-UP information incorporated above includes: On 27-Jul-2021: Patient details updated, new events were added. On 23-Sep-2021: Follow up document received updated event addition and outcome of event for arthritis.; Sender's Comments: This report concerns a 73 year old male patient with no relevant medical history who experienced non-serious and unexpected event of reactive arthritis of 1st and 2nd digits of his hands with decreased mobility (reported as could not open or close or make a fist). The event occurred after an unknown duration following vaccination with first dose of mRNA-1273. The patient reported not taking the 2nd dose of the vaccine in fear of re-occurrence of the event (coded as product dose omission).  The re-challenge was assessed as not applicable as the second dose was not administered. The benefit-risk relationship of mRNA-1273 is not affected by this report.