I hate shots because the stuff in them hurt. Blood draws, I've never had the courage to actually look at the needle going into my skin but once it's there I've no issues. I've had so many blood draws that the cumulative scars on the preferred vein look like a single scar measuring ½ inch by ¼ inch. (I sometimes wonder if people looking at my arm think I'm a drug user.)
While my daughter was too young to have a conscious memory, one of the doctors she saw did confirm that this almost certainly triggered the phobia. She was a year old, got sick, got dehydrated and it was determined she needed IV fluids. Between the doctor and the emergency room they missed the vein 12 times. When trying for the 13th IV stick they told me if that missed they would have to insert it in her jugular and that meant admittance to the hospital. Well lucky #13 worked.
I had one missed IV in my site and that was horrifically painful. I can't imagine what pain my little baby endured. But while she's gotten a lot better (imagine a 3-5 year old child successfully fighting off three grown adults when blood needed to be drawn) her phobia tells her "this immediate horror is much worse than the theoretical risk of what's being warded off."