Among those who contract infl uenza, subsequent illness and death may be infl uenced by underlying factors and conditions and by the timeliness and effectiveness of various treatment modalities. Most infl uenza illnesses are self-limiting, and most infected persons during both annual infl uenza epidemics and infl uenza pandemics (including that of 1918-19) recover with only supportive care in the community. Even so, current planning efforts recognize the potential importance of reducing disease during a pandemic, through early treatment with antiviral drugs and through other forms of treatment such as respiratory support and antimicrobial agents to treat secondary bacterial pneumonia, among those with more severe disease.