[DiogenesKynikos]

Without pre-existing immunity, a much larger fraction of the population would get flu each year. That's one of the primary reasons why people worry about pandemic flu, as opposed to the regular seasonal flu. An entirely new strain has the potential to infect a much larger share of the population than the regular seasonal flu, precisely because there's no pre-existing immunity.

> chances are 15% of us have already had it according to the Gangelt survey.

No, that's a completely unfounded conclusion to draw from that study. Gangelt was chosen precisely because it was an extremely hard-hit town. Researchers wanted wanted good statistics, so they went to the place that has the largest case density. There was an early superspreading event in Gangelt, during Carnival celebrations back in February. Hundreds of people came into close contact with a known infected person. The population of the town is only 12,000 to begin with.