Editor-In-Chief: C. Michael Gibson, M.S., M.D. 
In virology, superinfection is the process by which a cell that has previously been infected by one virus gets coinfected with another virus at a later point in time.
In medicine, superinfection is an infection following a previous infection, especially when caused by microorganisms that are resistant or have become resistant to the antibiotics used earlier.
Superinfection, according to Dorland's illustrated medical dictionary, is a condition produced by sudden growth of a type of bacteria, different from the original offenders in a wound or lesion under treatment.
Superinfection in Lambda phage
When a cell is a lambda lysogen, another lamda phage that infects is not able to undergo lytic development and produce phage. The incoming phage can inject DNA, however, the DNA is immediately shut down and no transcription/translation of the lambda initiates. Therefore, lambda lysogens are immune to infection by another lambda phage particle. The reason is because the lysogen is continuously producing cI repressor. The amount of cI protein exceeds the amount needed to shut down more than one phage. The extra repressor binds to the superinfecting phage DNA and prevents its transcription.