Breakthrough infection was observed in a patient, 49 days after the first dose; Patient tested positive for monkeypox 49 days after receiving the first dose of the MVA-BN; Breakthrough infection was observed in a patient, 49 days after the first dose; Literature citation.  Case reference number US-BN-2022-004056 is a literature case report, title as stated above, identified on 11-Oct-2022 and concerns an adult male patient of unknown age.  The clinic began administering MVA-BN (modified vaccinia ankara  bavarian nordic live virus (live-attenuated, non-replicating) to eligible individuals on 28-Jun-2022. Patients who tested positive for monkeypox at least 1 day after receiving the first dose of the MVA-BN from 28-Jun-2022, through 9-Sep-2022, were included. During the study period, 400 patients tested positive for monkeypox, and 7339 individuals received their first dose of MVA-BN. Ninety patients tested positive for monkeypox at least 1 day after vaccination with a median age of 33 years (IQR, 29-41; range, 24-69 years); 91 percent were cisgender men, 37.8 percent were living with HIV, and 73.5 percent had viral loads less than 200 copies/mL.  Eight monkeypox cases occurred more than 28 days from the first dose of MVA-BN, of which 2 cases occurred more than 14 days from the second dose. All 8 patients self-identified as cisgender males, 50 percent (4/8) had HIV, all of whom were virologically suppressed. All patients except 1 had fewer than 10 lesions. At least two breakthrough infections were observed in individuals at least three weeks after a second dose. One patient had a breakthrough infection 49 days after the first dose that is, 21 days after the second dose, the patient had systemic symptoms like fatigue and lymphadenopathy and perianal lesion (less than 10).  This case is linked to the cases US-BN-2022-004048, US-BN-2022-004050, US-BN-2022-004051, US-BN-2022-004052, US-BN-2022-004053, US-BN-2022-004054, US-BN-2022-004055 and US-BN-2022-004059 (same reporter).  Additional information received from Bavarian Nordic on 11-Oct-2022 included local BN case ID.; Reporter's Comments: An adult male patient of unknown age developed the serious (medically significant) event of monkeypox (also considered breakthrough infection, which is serious and medically significant, and vaccination failure), 49 days after the first dose, equivalent to 21 days after the second dose of MVA-BN. The patient had fatigue and lymphadenopathy, as well as less than 10 perianal lesions. Breakthrough infection, monkeypox and vaccination failure are unlisted per the RA V1.0 and RA for MVA-BN. Medical history and concomitant medications information was not available. Considering that the vaccine is non-replicating and does not contain monkeypox virus, and that the infection occurred 21 (more than 14 days later) days after the second dose, the event of monkeypox is assessed as not related to MVA-BN. This case may represent a lack of efficacy since the monkeypox infection occurred 3 weeks after the second dose of Jynneos. Therefore, vaccination failure and breakthrough infection are assessed as related.; Sender's Comments: An adult male patient of unknown age developed the serious (medically significant) event of monkeypox (also considered breakthrough infection, which is serious and medically significant, and vaccination failure), 49 days after the first dose, equivalent to 21 days after the second dose of MVA-BN. The patient had fatigue and lymphadenopathy, as well as less than 10 perianal lesions. Breakthrough infection, monkeypox and vaccination failure are unlisted per the RA V1.0 and RA for MVA-BN. Medical history and concomitant medications information was not available. Considering that the vaccine is non-replicating and does not contain monkeypox virus, and that the infection occurred 21 (more than 14 days later) days after the second dose, the event of monkeypox is assessed as not related to MVA-BN. This case may represent a lack of efficacy since the monkeypox infection occurred 3 weeks after the second dose of Jynneos. Therefore, vaccination failure and breakthrough infection are assessed as related.