Symptoms returned 2 days after last dose of Paxlovid. Tested positive again after testing negative; Pfizer/BioNTech Dose Number: 2 on 15Apr2021; Moderna Dose Number: 3 on 29Nov2021; This spontaneous case was reported by a consumer and describes the occurrence of COVID-19 (Symptoms returned 2 days after last dose of Paxlovid. Tested positive again after testing negative) and INTERCHANGE OF VACCINE PRODUCTS (Pfizer/BioNTech Dose Number: 2 on 15Apr2021; Moderna Dose Number: 3 on 29Nov2021) in a 49-year-old female patient who received mRNA-1273 (Moderna COVID-19 Vaccine) for COVID-19 vaccination.     The patient's past medical history included Drug allergy. Previously administered products included for Product used for unknown indication: Pfizer / BioNTech (Dose Number: 2 Location of injection: Arm Left) on 15-Apr-2021. Past adverse reactions to the above products included No adverse event with Pfizer / BioNTech.    On 29-Nov-2021, the patient received third dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) 1 dosage form. On 29-Nov-2021, the patient experienced INTERCHANGE OF VACCINE PRODUCTS (Pfizer/BioNTech Dose Number: 2 on 15Apr2021; Moderna Dose Number: 3 on 29Nov2021). On 18-May-2022, the patient experienced COVID-19 (Symptoms returned 2 days after last dose of Paxlovid. Tested positive again after testing negative). The patient was treated with NIRMATRELVIR, RITONAVIR (PAXLOVID) from 11-May-2022 to 16-May-2022 for COVID-19 treatment, at an unspecified dose and frequency. In May 2022, COVID-19 (Symptoms returned 2 days after last dose of Paxlovid. Tested positive again after testing negative) had resolved. At the time of the report, INTERCHANGE OF VACCINE PRODUCTS (Pfizer/BioNTech Dose Number: 2 on 15Apr2021; Moderna Dose Number: 3 on 29Nov2021) had resolved.      DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): On 18-May-2022, SARS-CoV-2 test: positive (Positive) Positive. On an unknown date, SARS-CoV-2 test: negative (Negative) Negative.         No concomitant medication was reported.  Patient was not taking any other medications or products within 2 weeks of starting COVID-19 treatment. Device date was reported as 18May2022.  Company Comment: This is a spontaneous case of interchange of vaccine products for this 49-year-old, female patient with past drug history of administration of the second dose of the Pfizer/BioNTech COVID-19 mRNA vaccine, who experienced the unexpected, non-serious AESI of COVID-19. The event occurred approximately 5 months after receiving the third dose of the mRNA-1273 vaccine. The patient tested positive for SARS-CoV-2 on an unspecified date. No symptoms were reported. She took and completed a 6-day course of Paxlovid (nirmatrelvir, ritonavir) from 11May2022 to 16May2022. It was reported that the symptoms (unspecified) recurred 2 days after the last dose of Paxlovid. The patient again tested positive for SARS-CoV-2 after testing negative on an unspecified date. No additional details were provided at the time of the report. The benefit-risk relationship of the mRNA-1273 vaccine is not affected by this report.; Sender's Comments: This is a spontaneous case of interchange of vaccine products for this 49-year-old, female patient with past drug history of administration of the second dose of the Pfizer/BioNTech COVID-19 mRNA vaccine, who experienced the unexpected, non-serious AESI of COVID-19. The event occurred approximately 5 months after receiving the third dose of the mRNA-1273 vaccine. The patient tested positive for SARS-CoV-2 on an unspecified date. No symptoms were reported. She took and completed a 6-day course of Paxlovid (nirmatrelvir, ritonavir) from 11May2022 to 16May2022. It was reported that the symptoms (unspecified) recurred 2 days after the last dose of Paxlovid. The patient again tested positive for SARS-CoV-2 after testing negative on an unspecified date. No additional details were provided at the time of the report. The benefit-risk relationship of the mRNA-1273 vaccine is not affected by this report.