Here is some research on the efficacy of Copper to control FB from Cornell. The article also recommends that blooms be removed on first and second year trees, because they can be permanently damaged when the FB bacteria gets to the leader.
FB really is mysterious. I’m in a climate very prone to FB and I struggle with it every year. My worst case was on second and third year trees a few years ago. FB is a good reason not to grow apples, especially in a hot humid climate like mine where heavy dew or rain during the bloom period are normal.
http://nyshs.org/wp-content/uploads/2016/10/Successful-Fire-Blight-Control-is-in-the-Details.pdf