I convalescent l have8 days l was on the hospital for one surgery; I convalescent l have8 days l was on the hospital for one surgery; And today like a ball came out behind my knee. Like if it was a little bag of skin, like something coming out behind my right knee.; I am worried because the first day I got the vaccine I felt my veins were going to explode and this lasted for about two days; This spontaneous case was reported by a patient (subsequently medically confirmed) and describes the occurrence of SURGERY (I convalescent l have8 days l was on the hospital for one surgery) and CONVALESCENT (I convalescent l have8 days l was on the hospital for one surgery) in a 42-year-old female patient who received mRNA-1273 (Moderna COVID-19 Vaccine) (batch no. 014C21A) for COVID-19 vaccination. The occurrence of additional non-serious events is detailed below.     No Medical History information was reported.    On 15-May-2021, the patient received first dose of mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular) 1 dosage form. On 15-May-2021, the patient experienced VASCULAR PAIN (I am worried because the first day I got the vaccine I felt my veins were going to explode and this lasted for about two days). On 20-May-2021, the patient experienced SKIN MASS (And today like a ball came out behind my knee. Like if it was a little bag of skin, like something coming out behind my right knee.). On an unknown date, the patient experienced SURGERY (I convalescent l have8 days l was on the hospital for one surgery) (seriousness criterion hospitalization) and CONVALESCENT (I convalescent l have8 days l was on the hospital for one surgery) (seriousness criterion hospitalization). The patient was hospitalized for 8 days due to SURGERY. The patient was treated with ASPIRIN [ACETYLSALICYLIC ACID] at an unspecified dose and frequency. On 17-May-2021, VASCULAR PAIN (I am worried because the first day I got the vaccine I felt my veins were going to explode and this lasted for about two days) had resolved. At the time of the report, SURGERY (I convalescent l have8 days l was on the hospital for one surgery), CONVALESCENT (I convalescent l have8 days l was on the hospital for one surgery) and SKIN MASS (And today like a ball came out behind my knee. Like if it was a little bag of skin, like something coming out behind my right knee.) outcome was unknown.        The action taken with mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular) was unknown.       No concomitant medication provided. No treatment information was provided. She was hospitalized and underwent surgery to detect if cancer is there or not. Not much details are provided.  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.   Most recent FOLLOW-UP information incorporated above includes: On 14-Jul-2021: Added new events convalescent and surgery. Case upgraded to serious as per FU with seriousness criteria hospitalization.; 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.