Swine flu killed a couple hundred thousand only 10 years ago or so. There were a pair of flu pandemics each lasting about a year, one in the 1950s, and one in the 60s. Each of those killed a million.

The Spanish flu killed like ?? tens of millions, also in a year or two.

There was a more protracted pandemic that killed a million around 1910-1920, but it wasn't a flu.