The present invention relates to a fowlpox virus genome which has modifications in one or more wild-type FPV genes. The present invention also relates to a viral particle comprising such a genome and its use to deliver a nucleotide of interest (NOI) to a target cell. The present invention also relates to vaccination methods, particularly a method which comprises administering a priming composition (which comprises a first non-replicating viral vector) and a boosting composition (which comprises a second non-replicating viral vector) to a subject to treat and/or prevent a disease.