The same year. What started as a bad flu in Kansas in the Spring of 1918 morphed into a super-killer by the Fall of the same year.[0]

[0]https://www.history.com/news/spanish-flu-second-wave-resurge...

yes - the first wave appeared to use young people as a transmission vector but didn't harm them compared to the second and third waves where they were hammered as hard as the young and old.