Vaccination adverse reaction; White blood cell count low; Fever; shaking; chills; vomiting; White blood Cell count low; This spontaneous case was reported by a physician (subsequently medically confirmed) and describes the occurrence of WHITE BLOOD CELL COUNT DECREASED (White blood cell count low), WHITE BLOOD CELL COUNT DECREASED (White blood Cell count low), PYREXIA (Fever), TREMOR (shaking), CHILLS (chills), VOMITING (vomiting) and VACCINATION COMPLICATION (Vaccination adverse reaction) in a 66-year-old male patient who received mRNA-1273 (Moderna COVID-19 Vaccine) for COVID-19 vaccination.     The patient's past medical history included Acute myeloid leukemia. Concomitant products included VENETOCLAX (VENCLEXTA) for Acute myeloid leukemia, APIXABAN (ELIQUIS), FLUOXETINE HYDROCHLORIDE (PROZAC), ACICLOVIR SODIUM (ACYCLOVIR [ACICLOVIR SODIUM]), METRONIDAZOLE (FLAGYL [METRONIDAZOLE]), ALPRAZOLAM (XANAX), OXYCODONE, TRAZODONE, POSACONAZOLE (NOXAFIL), LEVOFLOXACINE [LEVOFLOXACIN] and SENNA ALEXANDRINA (SENNA PLUS [SENNA ALEXANDRINA]) for an unknown indication.    On 30-Mar-2021, the patient received first dose of mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular) 1 dosage form. In March 2021, the patient experienced WHITE BLOOD CELL COUNT DECREASED (White blood Cell count low) (seriousness criterion hospitalization), PYREXIA (Fever) (seriousness criterion hospitalization), TREMOR (shaking) (seriousness criterion hospitalization), CHILLS (chills) (seriousness criterion hospitalization) and VOMITING (vomiting) (seriousness criterion hospitalization). In April 2021, the patient experienced WHITE BLOOD CELL COUNT DECREASED (White blood cell count low) (seriousness criterion hospitalization). On an unknown date, the patient experienced VACCINATION COMPLICATION (Vaccination adverse reaction) (seriousness criterion hospitalization). The patient was hospitalized for 2 days due to CHILLS, PYREXIA, TREMOR, VACCINATION COMPLICATION, VOMITING and WHITE BLOOD CELL COUNT DECREASED. At the time of the report, WHITE BLOOD CELL COUNT DECREASED (White blood cell count low) and WHITE BLOOD CELL COUNT DECREASED (White blood Cell count low) had not resolved, PYREXIA (Fever), TREMOR (shaking), CHILLS (chills) and VOMITING (vomiting) had resolved and VACCINATION COMPLICATION (Vaccination adverse reaction) outcome was unknown.      DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): In March 2021, Blood test: wbc decreased (Low) white blood cell count low. In March 2021, Body temperature: 103 (Inconclusive) 103 no unit. In April 2021, Blood test: wbc decreased (Low) white blood cell count low.     The action taken with mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular) was unknown.   For mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular), the reporter did not provide any causality assessments.   The patient was treated with Flagyl and Demrol.  Based on current available information and the temporal association between product use and the start date of the events a causal relationship cannot be excluded.; Sender's Comments: Based on current available information and the temporal association between product use and the start date of the events a causal relationship cannot be excluded.