I think the horrid conditions of World War I had more to do with the spread of the Spanish Flu than El Nino.
No horrid war conditions in the U.S. It seems to be true that the flu started in the the U.S. and spread to Europe through our soldiers. And apparently spread elsewhere from Europe.
They're saying it hit India hard and probably due to their drought. Maybe more so due to their population density.
Still lots of speculation here.