HYPERTENSIVE CRISIS; This 72-year-old, female subject was participating in a study and experienced the life-threatening event of hypertensive crisis.    The subject's medical history, as provided by the investigator, included body aches  generalized, thyroidectomy, inflammation  generalized, granuloma annulare, depression, hypertension, hyperlipidemia, hypothyroidism, recurrent urinary tract infection (UTI), postmenopausal, and seasonal allergies. Concomitant medications included azelastine hydrochloride, flunisolide, ibuprofen, meloxicam, influenza vaccine, levothyroxine, bupropion hydrochloride, atenolol, fluoxetine hydrochloride, atorvastatin, multivitamin, vaccinium macrocarpon, and cetirizine.   The subject was randomized to receive blinded intramuscular mRNA-1273 for SARS-CoV-2 vaccination and was unblinded on 21 Jan 2021. The subject received the first dose of mRNA-1273 on 21 Oct 2020. The subject received the second dose of mRNA-1273 on 18 Nov 2020. The subject received the booster dose of mRNA-1273 on 10 Nov 2021. The subject's last dose of mRNA-1273 prior to event onset was on the same day of the event, 10 Nov 2021 at 1440.   On 10 Nov 2021, the subject experienced hypertensive crisis. It was noted that the subject had a baseline condition of mild hypertension. Following booster dose vaccination on 10 Nov 2021, the subject's blood pressure elevated to 185/79 at 1511, then continued to rise and was 215/97 at 1542. The subject was sent to the emergency department (ED) for urgent care for stroke risk, was still in the ED at the time of the report.  No treatment information was reported by the investigator.    No action was taken with the study drug in response to the event.   The event, hypertensive crisis, was reported as not resolved.   The investigator assessed the event, hypertensive crisis, as related to study drug and not related to study procedure.  On 12-Nov-2021, the safety database was searched for events similar to Hypertensive crisis using the following search criteria: HLGT: Vascular hypertensive disorders.   As of 12-Nov-2021 under IND 019745 for mRNA-1273, 17 similar events were retrieved, including the current index case.  * Case MOD-2021-223852: Reported and Determined causality are in blank in the "Search results report"; however, in the case Reported and Determined causality are "Not related".  None of these cases reporting the following events were previously submitted as IND Safety Reports.  There were 16 cases that were non-IND Safety Reports (expected and related or unexpected and unrelated or expected and unrelated to the IMP) reporting the following events: PT: Hypertension: 9 (MOD-2020-000285, MOD-2020-000418, MOD-2020-000514, MOD-2020-001177, MOD-2021-015200, MOD-2021-018529, MOD-2021-121680, MOD-2021-223852, MOD-2021-288667); PT: Hypertensive emergency: 2 (MOD-2020-000301, MOD-2020-000307), PT: Hypertensive urgency 5 (MOD-2020-000225, MOD-2020-000356, MOD-2021-003115, MOD-2021-294681, MOD-2021-324970). MOD-2021-223852  In all these cases, the events PT: Hypertension, Hypertensive emergency and Hypertensive urgency were considered as not related to the study vaccine by the PI and the sponsor; out of these 16 cases, there is one case (MOD-2020-000301) in which the event developed almost 30 min after the vaccine administration, in a similar context as the index case.  Case MOD-2020-000301 concerns a 55-year-old female with a medical history of hypertension, severe obesity, atrial fibrillation, gallbladder removal, sleeve gastrectomy, cardiac ablation, right ovary and tube removed, right knee arthroscopy, anemia, mild asthma and menopause who experienced an unexpected event of hypertensive emergency.  The event occurred during 30 minutes after the first dose of the study medication and was considered life threatening. Other than the elevated blood pressure, the subject had no other symptoms of hypertensive emergency. It was recommended that the subject go to the emergency department (ED). Her cardiologist was contacted, and stated the subject had been non-compliant with medications and recommended ED admission. She was treated with oral lisinopril. She remained asymptomatic and declined EMS transport and ED admission. The event was considered unrelated to the study medication in agreement with the Investigator's assessment, and explained by the patient's non-compliance with medications reported by her cardiologist  The index case (Case ID: MOD-2021-382157) concerns a 72-year-old, female subject with relevant medical history of depression, hypertension, hyperlipidemia, hypothyroidism, recurrent urinary tract infection and postmenopausal who experienced the unexpected event of hypertensive crisis, considered as life-threatening. The event occurred 12 months 11 days after the first dose of the study vaccine, 11 months 21 days after the second dose and on the same day of the booster dose, approximately, 30 min after the vaccine administration. The event, hypertensive crisis, was reported as not resolved. The event was considered related to IP in agreement with the Investigator based on close temporal association with the administration of the vaccine. Medical history of hypertension is a confounder. Additional information was requested.  The 2 cases occurred in subjects with history of hypertension, both post-menopausal females and with other co-morbidities. Both events happened 30 minutes after dosing. In the first case, the event happened after the first dose, and it was clear that the subject had been non-complaint with her hypertension medications, as reported by her Cardiologist. In the index case, the event happened with the third dose but not with the first or second doses. Also, there is no information indicating non-compliance with her medications, however that has to be confirmed by the Investigator.  Based on review of available data, and close temporal association, the Sponsor cannot rule out a possible cause and effect relationship between administration of mRNA-1273 and the occurrence Crisis hypertensive. The subject's history of hypertension, as well as other potential confounders like hypertension treatment lack of compliance, and emotional distress (still to be confirmed), could have contributed to the event.   After review of the clinical details and investigator comments pertaining to this adverse event, and based upon experience to date, the Sponsor does not believe that changes to the conduct of this clinical trial are warranted. The Company will continue to monitor these and other serious adverse events reported in association with the IMP and will communicate any relevant changes to the protocol, Informed Consent Form, Investigator's Brochure, and/or Core Safety Information.; Reporter's Comments: This case concerns a 72-year-old, female subject with relevant medical history of depression, hypertension, hyperlipidemia, hypothyroidism, recurrent urinary tract infection and postmenopausal who experienced the unexpected event of hypertensive crisis, considered as life-threatening. The event occurred 12 months 11 days after the first dose of the study vaccine, 11 months 21 days after the second dose and on the same day of the booster dose, approximately, 30 min after the vaccine administration. No action was taken with the study drug in response to the event. The event, hypertensive crisis, was reported as not resolved. The event was considered related to IP in agreement with the Investigator based on close temporal association with the administration of the vaccine. Medical history of hypertension is a confounder. Additional information was requested.