Flu or Cold; The classic feeling of yucky; His body is developing blood clots; Severe reaction to the Moderna booster vaccine; Dizzy,very dizzy; Very tough to deal with; Can't walk; Can't think well; Pressure on the back side of his skull; This spontaneous case was reported by a consumer and describes the occurrence of THROMBOSIS (His body is developing blood clots) in a 67-year-old male patient who received mRNA-1273 (Moderna COVID-19 Vaccine) for COVID-19 vaccination. The occurrence of additional non-serious events is detailed below.     No Medical History information was reported.    On 25-Oct-2021, the patient received third dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) 1 dosage form. In October 2021, the patient experienced THROMBOSIS (His body is developing blood clots) (seriousness criterion medically significant), VACCINATION COMPLICATION (Severe reaction to the Moderna booster vaccine), DIZZINESS (Dizzy,very dizzy), FEELING ABNORMAL (Very tough to deal with), GAIT DISTURBANCE (Can't walk), THINKING ABNORMAL (Can't think well) and HEAD DISCOMFORT (Pressure on the back side of his skull). On 26-Oct-2021, the patient experienced INFLUENZA LIKE ILLNESS (Flu or Cold) and NAUSEA (The classic feeling of yucky). At the time of the report, THROMBOSIS (His body is developing blood clots), VACCINATION COMPLICATION (Severe reaction to the Moderna booster vaccine), DIZZINESS (Dizzy,very dizzy), FEELING ABNORMAL (Very tough to deal with), GAIT DISTURBANCE (Can't walk), THINKING ABNORMAL (Can't think well), HEAD DISCOMFORT (Pressure on the back side of his skull), INFLUENZA LIKE ILLNESS (Flu or Cold) and NAUSEA (The classic feeling of yucky) outcome was unknown.        For mRNA-1273 (Moderna COVID-19 Vaccine) (Unknown), the reporter did not provide any causality assessments.   The patient stated that he received his first dose of Moderna COVID-19 Vaccine on 02-Mar-2021 and second dose on 02-Apr-2021. He got the Moderna booster on 25-Oct-2021.   The patient reported no reaction to the first two shots. But, he had a severe reaction to the Moderna booster vaccine. The patient states that he was dizzy, can't walk, and very tough to deal with.   The patient states that he can't think well. He had pressure on the back side of his skull, that made him very dizzy. The first day after the vaccine, he felt the classic feeling of yucky, had the flu or cold, which he expected. Since then the dizziness set it; it's very bad.   The patient stated that he visited doctor's office at the time of call because his cardiologist thinks it is a reaction.  The patient also reported that his body is developing blood clots.  No concomitant product use was provided by the reporter.    No treatment medications were reported.  Company comment: This case concerns a 67-year-old, male patient with no previous relevant medical history reported, who experienced the unexpected event of thrombosis. The event occurred on an unknown number of days after the third dose of mRNA-1273 Moderna vaccine. The rechallenge was not applicable since the event happened after the third dose. The benefit-risk relationship of mRNA-1273 Moderna vaccine is not affected by this report.   Most recent FOLLOW-UP information incorporated above includes: On 30-Oct-2021: Significant follow-up. Event-Thrombosis added.; Sender's Comments: This case concerns a 67-year-old, male patient with no previous relevant medical history reported, who experienced the unexpected event of thrombosis. The event occurred on an unknown number of days after the third dose of mRNA-1273 Moderna vaccine. The rechallenge was not applicable since the event happened after the third dose. The benefit-risk relationship of mRNA-1273 Moderna vaccine is not affected by this report.