Herein is described a modified viral vector comprising: a coat protein modified, for example by the addition of a cysteine residue, such that the modified viral vector yields less soluble virus relative to that from an unmodified viral vector upon extraction of plant material infected with the modified viral vector, thereby facilitating purification of a recombinant protein expressed from the modified viral vector. Also described is a method of reducing viral coat protein impurities during purification of a recombinant protein, a method of biocontainment for a recombinant viral vector, and a method of generating virus inoculum for the modified viral vector.