potassium level was dangerously low (2.5); broken out in a rash that itches like crazy - from skull to toes; throat is closing up; can't swallow, drink or eat anything; Can't get the second dose; exhausted/tired; really sick; dry heaving so bad that her rib cage hurt; couldn't really eat for about a week; allergic to vaccine; Rib cage hurt; pink blotches in whole body; A spontaneous report was received from consumer, who was the husband of a 77-years-old  patient who received Moderna's COVID-19 vaccine (mRNA-1273) and experienced events really sick (vaccine complication), exhausted/tired (fatigue), dry heaving so bad that her rib cage hurt (retching), couldn't really eat for about a week (feeding disorder), potassium level was dangerously low (2.5) (blood potassium decreased), broken out in a rash that itches like crazy - from skull to toes/rash which almost looks like shingles, but it is not (rash pruritic), allergic to the vaccine (vaccination complication), throat is closing up (throat tightness), can't swallow, drink or eat anything (dysphagia),rib cage hurt (chest pain), can't get the second dose (intentional dose omission), and pink blotches in whole body (rash macular).  The patient's medical history included allergy to morphine. Concomitant medications reported were hydrochlorothiazide, topiramate, tramadol, amlodipine, acetylsalicylic acid, alendronate sodium, and vitamins.  On 4 Mar 2021, prior to the onset of the events, the patient received their first of two planned doses of mRNA-1273 (lot/batch: 027A21A) Intramuscularly for prophylaxis of COVID-19 infection.  On 4 Mar 2021, a few hours after the injection, the patient was really sick and exhausted.  The husband stated, "you name it, she had it".  She was dry heaving so bad that her rib cage hurt.  Also, she couldn't really eat for about a week.  Her husband (the reporter) "tried to help with electrolytes".  The patient was also broken out in a rash that itched like crazy-from skull to toes.  The rash almost looked like shingles, but it was not (per the husband).   On 09 Mar 2021 (reported as after 5 days), he insisted the patient go to the walk-in clinic.  There, they drew up blood.  After a few hours they called back and told her to immediately go to the emergency room since her potassium level was "dangerously low" (2.5).  They told them that the patient could have a stroke so she was admitted until they could get her levels back up again.  In the hospital, they told the patient to take diphenhydramine hydrochloride "but they were worried about her levels, so they didn't pay attention to the rash."  They told her she was allergic to the vaccine and "can't get the second dose."  The husband said he had "never seen her so sick."  The patient was in the hospital until 10 Mar 2021 (reported as 2 days in the hospital) with intravenous (IV) potassium.  The reported said she was "still tired" after all that.  The husband called back a few minutes after his first call and said his wife told him her throat was closing up and she couldn't swallow, drink or eat anything.  He also reported that she had pink blotches in her whole body.  Treatment for the events included IV potassium and methylprednisolone 4 mg for 6 days.  Action taken with mRNA-1273 in response to the events was unknown.  The events of really sick, dry heaving so bad that her rib cage hurt, couldn't really eat for about a week, rib cage hurt, and potassium level was dangerously low (2.5) were considered resolved on 11 Mar 2021.   The events of exhausted/tired, broken out in a rash that itches like crazy-from skull to toes/ rash which almost looks like shingles, but it is not, pink blotches on body, allergic to vaccine, throat is closing up, can't get the second dose, and can't swallow, drink, or eat anything were considered not resolved at the time of this report.; Reporter's Comments: Based on the current available information and temporal association between the use of the product and the start date of the events, a causal relationship cannot be excluded.