Von Magnus phenomenon -

Abnormal replicative cycles of viruses Von Magnus phenomenon when cells are infected with a high dose of influenza virus, there is defective assembly during replication and the produced virus has high hemagglutinin titre but low infectivity. Abortive infection Due to defective maturation or assembly, either no release of virions occur or the progeny of a virus is noninfectious. Defective viruses Some viruses are genetically defective and require the help of simultaneously infected helper virus for replication. eg. HDV, Rous sarcoma virus.