My mother-in-law had an awful fever and dry cough unlike any I've ever seen in mid-February that lasted for ages. Chalked it up to the flu. Went to the doc and everything, but this was before Covid-19 had officially landed anywhere near us.

It's certainly possible that it's been around longer than expected, growing exponentially, hidden in the flu season, but we just recently reached the exponential turning point that makes it a big problem. It only starts killing when it's saturated enough of the population that the at-risk start dying in greater-than-usual numbers, which might take quite a while even with a relatively fast doubling rate.