COVID-19; Interchange of vaccine product; This spontaneous case was reported by a consumer and describes the occurrence of COVID-19 (COVID-19) in a  patient of an unknown age and gender who received mRNA-1273 (Moderna COVID-19 Vaccine) (batch no. 012H21B) for COVID-19 vaccination. The occurrence of additional non-serious events is detailed below.     The patient's past medical history included Breast cancer (Prior breast cancer) and Arrhythmia. Previously administered products included for Drug use for unknown indication: JANSSEN COVID-19 VACCINE (Dose Number: 1 Batch/Lot No: 041A21A) on 09-Apr-2021. Past adverse reactions to the above products included No adverse event with JANSSEN COVID-19 VACCINE. Concurrent medical conditions included Drug allergy (Allergy to unspecified drug.).    On 05-Dec-2021, the patient received second dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) 1 dosage form. On an unknown date, the patient experienced COVID-19 (COVID-19) (seriousness criterion medically significant) and INTERCHANGE OF VACCINE PRODUCTS (Interchange of vaccine product). The patient was treated with NIRMATRELVIR, RITONAVIR (PAXLOVID) from 22-May-2022 to 26-May-2022 for COVID-19 treatment, at an unspecified dose and frequency. At the time of the report, COVID-19 (COVID-19) was resolving and INTERCHANGE OF VACCINE PRODUCTS (Interchange of vaccine product) outcome was unknown.      DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): In May 2022, SARS-CoV-2 test: positive (Positive) At-home COVID test was very, very faint positive on day 10 with no symptoms and positive (Positive) On day 11, had strong positive home test again.         No concomitant medications were reported.   On 31-May-2022, the patient had COVID rebound. Initially patient's symptoms improved after taking Paxlovid and at-home COVID test was very, very faint positive on day 10 with no symptoms. On day 11, the patient had COVID symptoms including headache, sore throat, aches and pains with cough and wheezing were returned and had strong positive home test again. Later, patient received treatment with intravenous (IV) steroids, oral steroids, steroid inhaler, and B.  Company comment: This spontaneous case concerns a patient of an unknown age and gender, with no relevant medical history, who experienced the unexpected serious AESI of COVID-19 on an unknown date after receiving the mRNA-1273 vaccine as 2nd dose. Patient took Paxlovid for 5 days and symptoms improved after treatment. On day 10 from initiation of Paxlovid, patient became asymptomatic, and COVID test done at home was reported very faint positive. On day 11, COVID symptoms headache, sore throat, aches and pains, cough and wheezing returned, and SARS-CoV-2 test was reported positive. Steroids using various routes such as intravenous, oral, and via inhaler started as treatment regimen. The outcome of event was reported as resolving. The benefit-risk relationship of mRNA-1273 is not affected by this report. Event's seriousness was assessed based on medical judgement.   Reporter did not allow further contact; Sender's Comments: This spontaneous case concerns a patient of an unknown age and gender, with no relevant medical history, who experienced the unexpected serious AESI of COVID-19 on an unknown date after receiving the mRNA-1273 vaccine as 2nd dose. Patient took Paxlovid for 5 days and symptoms improved after treatment. On day 10 from initiation of Paxlovid, patient became asymptomatic, and COVID test done at home was reported very faint positive. On day 11, COVID symptoms headache, sore throat, aches and pains, cough and wheezing returned, and SARS-CoV-2 test was reported positive. Steroids using various routes such as intravenous, oral, and via inhaler started as treatment regimen. The outcome of event was reported as resolving. The benefit-risk relationship of mRNA-1273 is not affected by this report. Event's seriousness was assessed based on medical judgement.