No adverse event; Patient was given a 0.25 mL of Moderna Bivalent Booster dose instead of 0.5mL dose / Invalid Bivalent Dose Administered; This spontaneous case was reported by a nurse and describes the occurrence of ACCIDENTAL UNDERDOSE (Patient was given a 0.25 mL of Moderna Bivalent Booster dose instead of 0.5mL dose / Invalid Bivalent Dose Administered) and NO ADVERSE EVENT (No adverse event) in a 61-year-old male patient who received mRNA-1273 BIVALENT .222 (MODERNA COVID-19 VACCINE, BIVALENT (ORIGINAL AND OMICRON BA.4/BA.5)) for COVID-19 prophylaxis.     Patient had no known drug allergies. It was unknown if the patient ever been diagnosed with or tested positive for COVID-19. It was unknown if the patient had acute illnesses at the time of vaccination and up to one month before or any chronic or long-standing health conditions.     On 15-Sep-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 15-Sep-2022, the patient experienced ACCIDENTAL UNDERDOSE (Patient was given a 0.25 mL of Moderna Bivalent Booster dose instead of 0.5mL dose / Invalid Bivalent Dose Administered). On an unknown date, the patient experienced NO ADVERSE EVENT (No adverse event). At the time of the report, ACCIDENTAL UNDERDOSE (Patient was given a 0.25 mL of Moderna Bivalent Booster dose instead of 0.5mL dose / Invalid Bivalent Dose Administered) and NO ADVERSE EVENT (No adverse event) outcome was unknown. Not Provided      For mRNA-1273 BIVALENT .222 (MODERNA COVID-19 VACCINE, BIVALENT (ORIGINAL AND OMICRON BA.4/BA.5)) (Unknown), the reporter considered ACCIDENTAL UNDERDOSE (Patient was given a 0.25 mL of Moderna Bivalent Booster dose instead of 0.5mL dose / Invalid Bivalent Dose Administered) and NO ADVERSE EVENT (No adverse event) to be not related.    It was reported that prescriptions, over-the-counter medications, dietary supplements, or herbal remedies being taken at time of vaccination or at the time of the adverse event was unknown.   There were no other potential causes related to the event and it was unknown if the patient experienced a similar event in the past.   It was reported that the event did not cause the patient to seek medical care.   The nurse stated that she called and reported a dosing error on 27-Sep-2022. Then she got a follow up request for the information from Moderna. When she got the information, she realized that they put 2.5 ml administered but the administration error was actually 0.25 ml. Upon further follow up, it was reported that, Patient was given a 0.25 mL of Moderna Bivalent Booster dose on 15-Sep-2022.  The information was presented to staff on 27 Sep 2022.  Reportedly, the patient was called on 28 Sep 2022 and patient made aware received 0.25ml of bivalent booster dose. Patient verbalized understanding. Patient denied to go the emergency room or primary care provider and informed the patient according to moderna the recommendation was to re-vaccinate with full dose in 8 weeks from 15 Sep 2022.   Patient stated that he would to be re-vaccinated. Patient  was made aware and would reach out to patient regarding receiving full vaccination. Patient verbalized understanding.  Treatment medication was not provided by the reporter.