Spanish flu

The number of deaths was estimated to be at least 50 million worldwide with about 675,000 occurring in the United States.

https://www.cdc.gov/flu/pandemic-resources/1918-pandemic-h1n1.html#:~:text=It%20is%20estimated%20that%20about,occurring%20in%20the%20United%20States.

Which probably means full months had deadlier days than this list in the OP