This is a new virus for humans, so our bodies aren't programmed to recognize and attack these enemy germs when they invade. It takes time for the body's systems to recognize and then deal with such an unknown enemy.
To further complicate things, this germ doesn't make you show symptoms for longer than the influenza, before you do start to get sick, so you are contagious longer before you know to stay away from other people.
Also, this germ continues making you contagious for up to 5 weeks after you feel well, so again, you can be spreading it to others when you think you are already done with it.
Nice, huh?
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If a man does not keep pace with his companions, perhaps it is because he hears a different drummer.
Let him step to the music which he hears, however measured, or far away.--Henry David Thoreau