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.