The present invention addresses the need to improve the long-term storage stability (i.e. infectivity) of vector formulations. In particular, it has been demonstrated that for adenovirus, the use of bulking agents, cryoprotectants and lyoprotectants imparts desired properties that allow both lyophilized and liquid adenovirus formulations to be stored at 4.degree. C. for up to 6 months and retain an infectivity between 60 100% of the starting infectivity.