After seeing multiple physicians it was determined that her breast implants need to be removed as there is some infectious process going on; slight flu like symptoms; Side effects started with a sore arm; This spontaneous case was reported by a consumer and describes the occurrence of MASTITIS (After seeing multiple physicians it was determined that her breast implants need to be removed as there is some infectious process going on) in a 66-year-old female patient who received mRNA-1273 (Moderna COVID-19 Vaccine) (batch nos. 03T821A, 028L20A and 026L219) for COVID-19 vaccination. The occurrence of additional non-serious events is detailed below.     No Medical History information was reported.   On 29-Dec-2020, the patient received first dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) 1 dosage form. On 26-Jan-2021, received second dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) dosage was changed to 1 dosage form. On 19-Aug-2021, received third dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) dosage was changed to 1 dosage form. On an unknown date, the patient experienced MASTITIS (After seeing multiple physicians it was determined that her breast implants need to be removed as there is some infectious process going on) (seriousness criterion medically significant), INFLUENZA LIKE ILLNESS (slight flu like symptoms) and PAIN IN EXTREMITY (Side effects started with a sore arm). The patient was treated with CEFALEXIN (KEFLEX [CEFALEXIN]) ongoing since an unknown date for Adverse event, at an unspecified dose and frequency. At the time of the report, MASTITIS (After seeing multiple physicians it was determined that her breast implants need to be removed as there is some infectious process going on), INFLUENZA LIKE ILLNESS (slight flu like symptoms) and PAIN IN EXTREMITY (Side effects started with a sore arm) had not resolved.        For mRNA-1273 (Moderna COVID-19 Vaccine) (Unknown), the reporter did not provide any causality assessments.   Concomitant medication details was not provided. Patient was undergone biopsy, mammogram, ultrasound and results was not provided  It was determined that her breast implants need to be removed as there is some infectious process going on. The symptoms are ongoing. The reaction started around October 3 or 4.  This case concerns a 66-year-old, female patient, with no reported medical history, who experienced the unexpected, serious events of mastitis. The event occurred on an unknown date, approximately 1 and a half month after third, booster, dose of mRNA-1273 vaccine. The rechallenge is not applicable, as no additional dose is expected. The benefit-risk relation of the mRNA-1273 vaccine is not affected by this report. Event Mastitis was automatically upgraded as a Serious event as per RA list and kept as serious as per medical judgement, despite it was reported as non-serious.; Sender's Comments: This case concerns a 66-year-old, female patient, with no reported medical history, who experienced the unexpected, serious events of mastitis. The event occurred on an unknown date, approximately 1 and a half month after third, booster, dose of mRNA-1273 vaccine. The rechallenge is not applicable, as no additional dose is expected. The benefit-risk relation of the mRNA-1273 vaccine is not affected by this report. Event Mastitis was automatically upgraded as a Serious event as per RA list and kept as serious as per medical judgement, despite it was reported as non-serious.