No adverse event; 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 (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 (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 (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 (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 have not reported any adverse reactions at that time.   No treatment medication was provided.  This case contains information for the 4th 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-2022-666248, US-MODERNATX, INC.-MOD-2022-666249, US-MODERNATX, INC.-MOD-2022-666250, US-MODERNATX, INC.-MOD-2022-666252, US-MODERNATX, INC.-MOD-2022-666255, US-MODERNATX, INC.-MOD-2022-666279, US-MODERNATX, INC.-MOD-2022-666281, US-MODERNATX, INC.-MOD-2022-666282, US-MODERNATX, INC.-MOD-2022-666283 (Linked Report).; Sender's Comments:  US-MODERNATX, INC.-MOD-2022-666251:Same reporter US-MODERNATX, INC.-MOD-2022-666280:Same reporter US-MODERNATX, INC.-MOD-2022-666284:Same reporter US-MODERNATX, INC.-MOD-2022-666286:Same reporter US-MODERNATX, INC.-MOD-2022-666278:Same reporter US-MODERNATX, INC.-MOD-2022-666063:Same reporter US-MODERNATX, INC.-MOD-2022-666290:Same reporter US-MODERNATX, INC.-MOD-2022-666277:Same reporter US-MODERNATX, INC.-MOD-2022-666248:Same reporter US-MODERNATX, INC.-MOD-2022-666249:Same reporter US-MODERNATX, INC.-MOD-2022-666250:Same reporter US-MODERNATX, INC.-MOD-2022-666252:Same reporter US-MODERNATX, INC.-MOD-2022-666255:Same reporter US-MODERNATX, INC.-MOD-2022-666279:Same reporter US-MODERNATX, INC.-MOD-2022-666281:Same reporter US-MODERNATX, INC.-MOD-2022-666282:Same reporter US-MODERNATX, INC.-MOD-2022-666283:Same reporter