No adverse event; Patient received 0.25 mL dose instead of 0.5 mL dose/lower than authorized dose of Moderna bivalent vaccine administered to patients; This spontaneous case was reported by a pharmacist and describes the occurrence of ACCIDENTAL UNDERDOSE (Patient received 0.25 mL dose instead of 0.5 mL dose/lower than authorized dose of Moderna bivalent vaccine administered to patients) and NO ADVERSE EVENT (No adverse event) in an elderly patient of an unknown gender who received mRNA-1273 BIVALENT .222 (MODERNA COVID-19 VACCINE, BIVALENT (ORIGINAL AND OMICRON BA.4/BA.5)) (batch no. 061F22A) for COVID-19 prophylaxis.     No Medical History information was reported.    On 27-Oct-2022, the patient received dose of mRNA-1273 BIVALENT .222 (MODERNA COVID-19 VACCINE, BIVALENT (ORIGINAL AND OMICRON BA.4/BA.5)) (unknown route) .25 milliliter. On 27-Oct-2022, the patient experienced ACCIDENTAL UNDERDOSE (Patient received 0.25 mL dose instead of 0.5 mL dose/lower than authorized dose of Moderna bivalent vaccine administered to patients). On an unknown date, the patient experienced NO ADVERSE EVENT (No adverse event). At the time of the report, ACCIDENTAL UNDERDOSE (Patient received 0.25 mL dose instead of 0.5 mL dose/lower than authorized dose of Moderna bivalent vaccine administered to patients) and NO ADVERSE EVENT (No adverse event) outcome was unknown.        For mRNA-1273 BIVALENT .222 (MODERNA COVID-19 VACCINE, BIVALENT (ORIGINAL AND OMICRON BA.4/BA.5)) (Unknown), the reporter considered NO ADVERSE EVENT (No adverse event) to be not related. No further causality assessment was provided for ACCIDENTAL UNDERDOSE (Patient received 0.25 mL dose instead of 0.5 mL dose/lower than authorized dose of Moderna bivalent vaccine administered to patients).    No concomitant medications were provided. It was reported that 18 elderly patients received 0.25 mL dose instead of 0.5 mL dose The patients had not reported any adverse reactions at that time.  No treatment medication was provided. This case contains information for the 3rd of 18 elderly patients described by the reporter.   This case was linked to US-MODERNATX, INC.-MOD-2022-666277, US-MODERNATX, INC.-MOD-2022-666284, US-MODERNATX, INC.-MOD-2022-666280, US-MODERNATX, INC.-MOD-2022-666278, US-MODERNATX, INC.-MOD-2022-666286, US-MODERNATX, INC.-MOD-2022-666290, US-MODERNATX, INC.-MOD-2022-666063, US-MODERNATX, INC.-MOD-2022-666251, US-MODERNATX, INC.-MOD-2022-666295, US-MODERNATX, INC.-MOD-2022-666252, US-MODERNATX, INC.-MOD-2022-666248, US-MODERNATX, INC.-MOD-2022-666250, US-MODERNATX, INC.-MOD-2022-666255, US-MODERNATX, INC.-MOD-2022-666279, US-MODERNATX, INC.-MOD-2022-666283, US-MODERNATX, INC.-MOD-2022-666282 (E2B Linked Report).; Sender's Comments:  US-MODERNATX, INC.-MOD-2022-666277:Patient 7 US-MODERNATX, INC.-MOD-2022-666278:Patient 14 US-MODERNATX, INC.-MOD-2022-666286:Patient 10 US-MODERNATX, INC.-MOD-2022-666284:Patient 9 US-MODERNATX, INC.-MOD-2022-666290:Patient 11 US-MODERNATX, INC.-MOD-2022-666280:Patient 16 US-MODERNATX, INC.-MOD-2022-666063:Patient 1 US-MODERNATX, INC.-MOD-2022-666252:Patient 6 US-MODERNATX, INC.-MOD-2022-666251:Patient 5 US-MODERNATX, INC.-MOD-2022-666295:Patient 12 US-MODERNATX, INC.-MOD-2022-666248:Patient  2 US-MODERNATX, INC.-MOD-2022-666250:Patient 4 US-MODERNATX, INC.-MOD-2022-666255:Patient 13 US-MODERNATX, INC.-MOD-2022-666279:Patient 15 US-MODERNATX, INC.-MOD-2022-666283:Patient 8 US-MODERNATX, INC.-MOD-2022-666282:Patient 18