After rabbit hemorrhagic disease virus 2 (RHDV2) emerged in California in May 2020, an interagency/zoo/academia/non-profit team implemented emergency conservation actions to protect California’s Central Valley endemic, endangered riparian brush rabbit (Sylvilagus bachmani riparius, RBR). Vaccination of ~15% of the estimated RBR population began in September 2020 to minimize disease-caused extinction risk after a single dose vaccine trial on 19 wild RBRs temporarily held in captivity demonstrated safety. All trial RBRs developed antibodies, with titers from 1:10 - 1:160. Seroconversion generally occurred 7-10 days post-vaccine and antibody response was ≥60 days in 12 individuals. A total of 1,217 RBRs have been vaccinated at least once since 2020. Spatially explicit mark-recapture-based density estimates using capture data from Fall 2020-Spring 2022 ranged from 2.66- 62.52 RBRs/hectare. In Spring 2022, RHDV2-caused deaths of three unvaccinated RBRs and one sympatric desert cottontail (S. auduboni) confirmed species susceptibility to RHDV2. No mortalities in vaccinated RBRs were detected. Severe flooding January through June 2023 significantly reduced the RBR population, evidenced by reduced camera-trap detections and ~80% fewer RBR captures post-flood in October-November 2023 as compared to 2020-2022. Vaccination, disease surveillance, and population monitoring are ongoing to protect RBRs and monitor post-flood recovery.