They likely followed the same pattern. Severe initial outbreak when a new super strain appeared, then a gradual decline in severity as immunity developed and t

They likely followed the same pattern. Severe initial outbreak when a new super strain appeared, then a gradual decline in severity as immunity developed and the strain continued to evolve. Rinse and repeat. 1918 was the first time that a flu benefited from modern transportation speed and the massive movement of humanity to and from Europe because of the war. So in the past an equally deadly flu would inadvertently be contained simply because infected carriers couldn't move to new, uninfected areas before they were dead or and beaten the virus.