Interchange of vaccine products; severe flare of pemphigus vulgaris; This literature-non-study case was reported in a literature article and describes the occurrence of PEMPHIGUS (severe flare of pemphigus vulgaris) in a 46-year-old female patient who received mRNA-1273 (Moderna COVID-19 Vaccine) for COVID-19 vaccination. The occurrence of additional non-serious events is detailed below.       The patient's past medical history included Pemphigus vulgaris (history of pemphigus vulgaris, which had been in remission since undergoing 2 rituximab (1g) infusions in July and August of 2019.). Previously administered products included for Pemphigus vulgaris: Rituximab (undergone 2 rituximab (1g) infusions in July and August of 2019) in 2019. Past adverse reactions to the above products included No adverse event with Rituximab.    In May 2021, the patient received first dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) 1 dosage form. In 2021,  after starting mRNA-1273 (Moderna COVID-19 Vaccine), the patient experienced PEMPHIGUS (severe flare of pemphigus vulgaris) (seriousness criterion medically significant). On an unknown date, the patient experienced INTERCHANGE OF VACCINE PRODUCTS (Interchange of vaccine products). The patient was treated with PREDNISONE in 2021 for Pemphigus vulgaris, at a dose of 1 milligram/kilogram once a day and RITUXIMAB in 2021 for Pemphigus vulgaris, at a dose of 1 gram on day 1 and day 15. At the time of the report, PEMPHIGUS (severe flare of pemphigus vulgaris) was resolving and INTERCHANGE OF VACCINE PRODUCTS (Interchange of vaccine products) outcome was unknown. Related    DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): In 2021, Antibody test: 123 u/ml (High) significantly elevated at 123 U/mL and 105 u/ml (High) significantly elevated at 105 U/mL. In 2021, Dermatologic examination: abnormal Skin examination revealed numerous flaccid bullae and erosions on her trunk and extremities; yellow-crusted, eroded plaques on her scalp, and erosions of the oral mucosa.     For mRNA-1273 (Moderna COVID-19 Vaccine) (Unknown), the reporter considered PEMPHIGUS (severe flare of pemphigus vulgaris) to be related. No further causality assessment was provided for INTERCHANGE OF VACCINE PRODUCTS (Interchange of vaccine products).    Prior to vaccine, patient skin was clear, and not been on any immunosuppressive medications. At the time of her eruption, there were no other reports of pemphigus vulgaris associated with a COVID-19 vaccine in the literature. Given the uncertainty of whether a second dose of an mRNA vaccine could lead to an even more severe flare, the patient did not receive the second dose of the Moderna vaccine. However, the rise of the delta variant of SARS-CoV-2 prompted an in-depth discussion on the possible risks versus benefits of obtaining a vaccine from the alternative provider, Johnson & Johnson. The patient decided to proceed with receiving the Johnson & Johnson vaccine. She tolerated it well with no side effects nor pemphigus flare but remained on prednisone during this time. Although she improved with prednisone, her skin had not completely cleared. Thus, she was treated with rituximab 1 g on day 1 and day 15. She responded well and was able to be tapered off prednisone. Concomitant medications were not reported.  This literature-non-study case concerns a 46-year-old female patient, with medical history of pemphigus vulgaris, which had been in remission since undergoing 2 rituximab (1g) infusions in July and August of 2019, who experienced serious (medically significant) unexpected event of an acute and severe Pemphigus flare, which occurred 1 week after receiving the 1st dose of mRNA-1273 vaccine. Before, her skin was clear, and she had not been on any immunosuppressive medications. Skin examination revealed numerous flaccid bullae and erosions on her trunk and extremities; yellow-crusted, eroded plaques on her scalp, and erosions of the oral mucosa. Desmoglein 1 and 3 antibodies were significantly elevated at 123 U/mL and 105 U/mL respectively. The patient was started on a prednisone taper at 1 mg/kg/day. The mentioned medical history remains a confounder for the event. The benefit-risk relationship of the mRNA-1273 vaccine is not affected by this report.   Most recent FOLLOW-UP information incorporated above includes: On 31-Mar-2022: Follow up received by safety on 31-Mar-2022 has Email received from Regulatory Authority team and contains significant information: Literature information, lab data, patient details, suspect start date and treatment information updated; Sender's Comments: This literature-non-study case concerns a 46-year-old female patient, with medical history of pemphigus vulgaris, which had been in remission since undergoing 2 rituximab (1g) infusions in July and August of 2019, who experienced serious (medically significant) unexpected event of an acute and severe Pemphigus flare, which occurred 1 week after receiving the 1st dose of mRNA-1273 vaccine. Before, her skin was clear, and she had not been on any immunosuppressive medications. Skin examination revealed numerous flaccid bullae and erosions on her trunk and extremities; yellow-crusted, eroded plaques on her scalp, and erosions of the oral mucosa. Desmoglein 1 and 3 antibodies were significantly elevated at 123 U/mL and 105 U/mL respectively. The patient was started on a prednisone taper at 1 mg/kg/day. The mentioned medical history remains a confounder for the event. The benefit-risk relationship of the mRNA-1273 vaccine is not affected by this report.