One virus particle prevents multiplication of the second virus. This phenomena is -
Interference

In a mixed or multiple infection of cells, in which infection of a cell by one virus inhibits simultaneous or subsequent infection by another virus is called Interference.
The most important mediator of interference is interferon.
A high multiplicity of infection inhibits production of its own infectious progeny - autointerference
Viral interference has been applied in the field in Controlling poliomyelitis by live attenuated vaccine.
Viral interference
Mutation
Supervision
Permutation