Bovine respiratory syncytial virus (BRSV), a common cause of bovine respiratory disease (BRD) is closely related to human RSV. There is limited knowledge of immune parameters during infection, including impact on maternal antibodies, response to unrelated vaccinations and virus persistence. We examined immune responses to BRSV, maternal antibodies (BRSV/other BRD viruses), virus antigen/RNA up to 4 weeks post challenge in calves, and response to an unrelated vaccine.  Sixteen calves were assigned to 2 mixed breed groups, both vaccinated with a Sendai virus (SeV)-vectored eGFP mock, mucosal vaccine. Twenty-one days later 1 group was challenged with BRSV and 1 mock-challenged. Calves were euthanised 28 days later.  Throughout the study clinical signs/lung ultrasound were scored and blood/nasal samples taken. At PM, lung tissues/tracheobronchial lymph nodes (LN)/other tissues were harvested.  qRT-PCR was carried out on swabs/tissues. Serum was screened for IgG, IgM, IgA against BRSV/SeV/other BRD viruses (ELISA) and BRSV/SeV neutralising antibodies; nasal mucus for BRSV-specific IgA (ELISA); PBMCs for selected cytokines (ELISpot).   Some calves exhibited baseline lung lesions. The SeV vaccine did not induce clinical signs/pathology, indicating safety as a vaccine platform. BRSV RNA persisted in all calves. BRSV infection had no effect on maternal antibody decline rates or response to the vaccine. There were high levels of IgA (particularly mucosal IgA) in all calves, while IgG/neutralising antibody levels were variable. This study provides new knowledge about BRSV in and safety of a SeV-based vaccine vector system in calves.