A few years ago I got interested in my ancestry. I discovered a great great uncle, born in 1892, who immigrated to the U.S. from Romania in 1904 (aboard the RMS Carpathia, which would later become famous for rescuing the survivors of the Titanic in 1912 and was itself torpedoed and sunk in 1918).

His family likely left Romania due to the persecution Jews were experiencing in eastern Europe. Sadly, he died from the Flu in Denver, CO in 1918. :(

The 1918 flu pandemic also came at the tail end of World War 1, when the youngest and healthiest were in incredibly close proximity and likely had compromised immune systems from a few years of warfare.

And people had had less food than normal Germany especially had major food shortages.

> The theory is that that strain caused a larger immune response than typical flus, making it much deadlier.

For bonus points, this is suspected to be due to it triggering a "cytokine storm": https://en.wikipedia.org/wiki/Cytokine_storm