Now, it's unrealistic to assume that countries wouldn't do ANYTHING to fight the virus once people started dying.  So the Imperial College team ran the numbers again, this time assuming a "mitigation" strategy.  A mitigation strategy is pretty much what common sense would tell us to do: America places all symptomatic cases of the disease in isolation.  It quarantines their families for 14 days.  It orders all Americans over 70 to practice social distancing.  This is what you've seen a lot of people talking about when they say we should "flatten the curve": try to slow the spread of the disease to the people most likely to die from it, to avoid overwhelming hospitals.