It has to be pointed out that the numbers who die are likely to be relatively small. The 1918 flu only killed 2 or 3% in a day when oxygen was rarely used and respirators were even rarer. Medical science has advanced a bit since those days and survival is expected to be better.
2%-3% of the human population world-wide is not small number - medical resources are quickly overwhelmed. Modern survival rates for *a* patient in the US will be very good, but not necessarily for *10 million* patients.
Most major services, food delivery, garbage collection and power still worked and fuel got delivered.
In 1918 even the US was primary rural. Most people got *none* of the above services even in normal times: "food delivery" was the chicken walking into the house and fuel was whatever the horse ate.
our supply system may have gotten more fragile with on-hand supplies smaller and run closer to the edge by using JIT, Just In Time, supply schedules.
Again the difference is that we depend on a supply system at all. In 1918 most Americans didn't (for long periods; salt, sugar, etc, was traded when someone came through town) so the "system" had to cope with a much smaller number of people than it might seem.
Another difference will be the speed the disease spreads. In 1918 "Around The World In 80 Days" was not that far off the mark, but this time it's likely to take only a couple of weeks to do the same.