High blood pressure; Chills; This spontaneous case was reported by a patient and describes the occurrence of HYPERTENSION (High blood pressure) and CHILLS (Chills) in a 75-year-old male patient who received mRNA-1273.815 (SPIKEVAX 2023-2024) for COVID-19 prophylaxis.     Patient had electrical issues with heart was being watched since prior to receiving COVID-19 vaccination. Patient had never had high blood pressure and never took medications prior to Spikevax vaccination. He was healthy prior to vaccination. He had no issues, and no medications were prescribed.  Previously administered products included for Product used for unknown indication: Flu shot in August 2023. Past adverse reactions to the above products included No adverse event with Flu shot.    On 19-Oct-2023, the patient received sixth dose of mRNA-1273.815 (SPIKEVAX 2023-2024) (unknown route) 1 dosage form. On 20-Oct-2023,  after starting mRNA-1273.815 (SPIKEVAX 2023-2024), the patient experienced CHILLS (Chills). On 21-Oct-2023, the patient experienced HYPERTENSION (High blood pressure). The patient was treated with AMLODIPINE BESYLATE for Blood pressure high, at a dose of 5 milligram once a day. At the time of the report, HYPERTENSION (High blood pressure) had not resolved and CHILLS (Chills) outcome was unknown.      DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): On 21-Oct-2023, Blood pressure measurement: 2 Days after receiving Spikevax his blood pressure spiked up to about 158/92..     For mRNA-1273.815 (SPIKEVAX 2023-2024) (Unknown), the reporter did not provide any causality assessments.   No concomitant medications were reported.  It was unknown if patient receive any other vaccines in the 4 weeks prior to COVID-19 vaccine.  Patient stated he already received 6 Moderna COVID-19 shots and with first 5 doses he did not have any side effects, but with his last dose of Spikevax given a couple weeks ago, he experienced high blood pressure and visited to his doctor, who prescribed Amlodipine Besylate 5 mg, which was pretty standard medication for blood pressure issues. He also experienced a little bit of chills next day after the shot, but it was not too bad.  Patient was calling back because he forgot to report his BP increase and found out someone else had a similar experience after receiving Spikevax 2023-2024 Formula (Lot and expiration date was unknown).  Patient received Spikevax vaccine the Lot & Exp. date was unknown. 2 Days after receiving Spikevax his blood pressure spiked up to about 158/92. Patient had a Moderna shot and 1-2 days later his blood pressure spiked. He had never had high blood pressure before, now taking blood pressure medication.   This case was linked to US-MODERNATX, INC.-MOD-2023-748685.   Most recent FOLLOW-UP information incorporated above includes: On 08-Nov-2023: Live Follow up received that contain significant information includes added reporter, updated patient demographics, added medical history, added suspect product and event start date and updated narrative. On 08-Nov-2023: Live follow up received that contain non-significant information includes references were added. On 13-Nov-2023: Live follow up received that contain non-significant information includes references were added. On 13-Nov-2023: Live follow up received that contain non-significant information includes references were added. On 13-Nov-2023: Live follow up received that contain non-significant information includes references were added.; Sender's Comments:  US-MODERNATX, INC.-MOD-2023-748685:Different patient same product( Agent's wife case)