Review the replication cycle for flu viruses in Chapter 19. Pharmaceutical companies wish to produce antiviral drug therapies that can interrupt the viral replication cycle while causing minimal adverse effects on the host cells. Several classes of drugs are known to interrupt influenza A replication.

Oseltamivir (Tamiflu) and zanamivir (Relenza) are drugs that inhibit the action of the N protein. Oseltamivir has been used successfully in some cases but only during the first 36–48 hours postexposure. What part of viral replication is affected by these two drugs? Why is early treatment needed?