A recombinant virus may occur naturally or be produced by recombining pieces of DNA or RNA in a laboratory.
This may be used to produce viral vaccines or gene therapy vectors.
The term is also used to refer to naturally occurring recombination between virus genomes in a cell infected by more than one virus strain.
This occurs either by Homologous recombination of the nucleic acid strands or by reassortment of genomic segments.
In addition, reassortment is most important for pandemic influenza viruses.