minimal pericardial effusion; my oxygen saturation again plummeted/getting difficult to maintain my oxygen level during the day; mild arm pain; This spontaneous case was reported by a consumer (subsequently medically confirmed) and describes the occurrence of HYPOXIA (my oxygen saturation again plummeted/getting difficult to maintain my oxygen level during the day) and PERICARDIAL EFFUSION (minimal pericardial effusion) in a 69-year-old female patient who received mRNA-1273 (Moderna COVID-19 Vaccine) (batch nos. 026A21A and 03IL20A) for COVID-19 vaccination. The occurrence of additional non-serious events is detailed below.     The patient's past medical history included Hypoxia. Concurrent medical conditions included Pulmonary hypertension (Reporter states: Pulmonologists disagree about this diagnosis) since May 2019 and Sleep apnea since March 2019. Concomitant products included LORATADINE for Allergy, VITAMIN D3 and CYANOCOBALAMIN (VITAMIN B12 [CYANOCOBALAMIN]) for Deficiency vitamin.   On 05-Feb-2021 at 10:30 AM, the patient received first dose of mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular) 1 dosage form. On 05-Mar-2021 at 10:30 AM, received second dose of mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular) dosage was changed to 1 dosage form. On 05-Mar-2021,  after starting mRNA-1273 (Moderna COVID-19 Vaccine), the patient experienced PAIN IN EXTREMITY (mild arm pain). On 07-Mar-2021, the patient experienced HYPOXIA (my oxygen saturation again plummeted/getting difficult to maintain my oxygen level during the day) (seriousness criterion medically significant). On an unknown date, the patient experienced PERICARDIAL EFFUSION (minimal pericardial effusion) (seriousness criterion medically significant). At the time of the report, HYPOXIA (my oxygen saturation again plummeted/getting difficult to maintain my oxygen level during the day) and PERICARDIAL EFFUSION (minimal pericardial effusion) had not resolved and PAIN IN EXTREMITY (mild arm pain) outcome was unknown.      DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): On 07-Mar-2021, Oxygen saturation: low (Low) Low. On 17-Apr-2021, Brain natriuretic peptide: 1064 (High) "nearly 10 times the normal limit and is a strong indicator of heart failure". On 29-Apr-2021, Computerised tomogram thorax: abnormal (abnormal) minimal pericardial effusion.         Reporter states: I was diagnosed two years ago with sleep apnea and nocturnal hypoxia and have used a CPAP device with oxygen every night since. Following the first dose of the vaccine, my oxygen level was so low that I had to go onto daytime supplemental oxygen for the first time. After the second dose of the vaccine, my oxygen saturation again plummeted. I have been on 3-4 L of daytime supplemental oxygen ever since. It is getting difficult to maintain my oxygen level during the day even with supplemental oxygen. The cardiologist has ordered an echocardiogram for May 7, 2021. That should help determine if my breathing difficulties are due to a sudden worsening of pulmonary hypertension, or if this could be related to the vaccines.  Company Comment: 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.   This case was linked to MOD-2021-029767 (E2B Linked Report). This case was linked to MOD-2021-029686, MOD-2021-029686 (Patient Link).; Sender'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. MOD-2021-029767:Reporter's friend's case