[kazinator]

Viruses can mutate, changing their protein coating so as not to be recognized by your immune system. Why do you think the common cold has not gone away, or why new flu shots are needed every season?

We simply do not know what this virus will do.

The Spanish Flu pandemic of 1918 came in waves, and they were different.

[russholmes]

Immunity to coronaviruses does tend to fall within a year or so, but this is believed due to immune memory rather than viral mutation (coronaviruses have a modest mutation rate). This is a different mechanism than influenza. Subsequent reinfections are believed to be mild. A vaccine would provoke a longer immune memory by way of an adjuvant. Discussion of this in the TWIV podcast: http://www.microbe.tv/twiv/twiv-591/