Some theorized that the flu originated in the Far East. Dr. C. Hannoun, leading expert of the 1918 flu for the Institut Pasteur, asserted that the former virus was likely to have come from China, mutated in the United States near Boston, and spread to Brest, France, Europe's battlefields, Europe, and the world using Allied soldiers and sailors as main spreaders. Hannoun considered several other theories of origin, such as Spain, Kansas, and Brest, as being possible but not likely.

Historian Alfred W. Crosby speculated that the flu originated in Kansas. Political scientist Andrew Price-Smith published data from the Austrian archives suggesting that the influenza had earlier origins, beginning in Austria in the spring of 1917. Popular writer John Barry echoed Crosby in describing Haskell County, Kansas as the likely point of origin. Investigative work by a British team, led by virologist John Oxford of St Bartholomew's Hospital and the Royal London Hospital, has suggested that a major British troop staging camp in Étaples, France was at the center of the 1918 flu pandemic or was the location of a significant precursor virus.