The phylogenetic results, combined with these other lines of evidence, suggest that the high mortality in 1918 among adults aged ∼20 to ∼40 y may have been due primarily to their childhood exposure to a doubly heterosubtypic putative H3N8 virus, which we estimate circulated from ∼1889–1900. All other age groups (except immunologically naive infants) were likely partially protected by childhood exposure to N1 and/or H1-related antigens.
The Spanish flu apparently had the N1 complex present, to which the 20-40y population wasn’t exposed. At least that’s my limited understanding after skimming the paper.
No. However, the FDP are basically terrorists at this point and will stop at nothing to praise the „Schwarze Null“