This paper uses the SIR (Susceptible–Infectious–Recovered) model to help both researchers and policymakers better understand the spread and ultimate containment of an infection. In this model, those who recover are immune to the disease and thus the susceptible population declines over time. Using three groups — young (20–44), middle-aged (45–65) and older (65+) — the authors conduct a quantitative analysis of optimal policy. An approach that treats these three groups uniformly and involves a relatively strict, lengthy lockdown would result in both high economic damage and high mortality rates for older individuals. Better social outcomes are possible with targeted policies that treat these three age groups differently. For instance, a strict lockdown on the oldest group can minimize both economic losses and deaths.