So I was noticing the upward trend (quoted post) that began just slightly in 2006, and never fully went back down, which made me think—I'll bet the Fall of 2006 is when they really started pushing the flu vaccine for pregnant women. (It has about a 7x higher miscarriage rate, documented.)

I did a little digging and found the first randomized clinical trial looking at the flu vaccine in pregnancy was completed in 2005 (though it was not a placebo study, they compared two different vaccines and noted their apparent benefits) so... Bingo. Evidence in hand, they started pushing and touting the benefits the following "Flu season."

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7550856/