Abstract
The premature formation of a superinfecting poliovirus under conditions of heterotypic double-infection is reflected in the active replication of its RNA. During maturation, about 60 per cent of the RNA of the superinfecting virus becomes coated with capsids typical of the first infecting virus. This results in "genomic masking." About 40% of all progeny viruses contain the mixed serotypes of both parental viruses which implies that capsid proteins of the superinfecting virus have been synthesized as well.