Annual immunization is the most important preventive measure [40••] . However, two classes of antiviral drugs are available and play an important role in the treatment and prevention of influenza [41••] : the neuraminidase inhibitors (NI), oseltamivir and zanamivir, which are active against both influenza A and B viruses; and the M2 inhibitors, amantadine and rimantadine, which are active against all influenza A strains, but have no activity against influenza B viruses. In general, the duration for therapy with an NI is 5 days, and with the M2 inhibitors is three to 5 days.