I have one word for you - BRIBERY!!! We used to have a horrible time with our daughter (now 13) with shots and needles - and as she has chronic and severe medical problems, there are more needles in her life than in any twenty "healthy" kids (we are down to an average of two a week now). Here is what we do...for "big" sticks (painful shots, etc.) we would pick out something she really wanted (did not have to be expensive - a book, small toy, special treat) and bring it with us. The deal was that if she behaved and cooperated (She could cry, but no screaming, flailing or fighting.), she could have the reward. If not, it went back to the store. With smaller pokes, like routine blood draws, etc., she earned money - a quarter to a dollar, depending on the poke. She could save the money for a special treat or toy, but if she fought a nurse and kicked or hit or made their job really hard, she had to use some of her saved money for a card or small apology gift. It took a few times, but it has worked fantastically for us. Consistency is key - if she does not behave, you have to follow through and not give the reward or actually have her follow through with the apology, even when it means it upsets her again.
The hardest part as a parent is watching your child in pain, whether from the needle or the panic, but you have to remember that you are being a good parent, and you are doing what is best for them. Better a needle stick and a few tears now than a debilitating or fatal illness later. Best of luck to you!