Ill Health has plague mankind for many years. In history there are so many accounts of mortality rates being high in comparaison to today.
Today we have come along way to combat illness through the advance of science and research. Such medicines as penicillin, and insulin along with many other medical advances has improved our longevity. This was not due to prayers, it was due to taking the initiative and our creativity.
There is a study that is being conducted on prosthetics (limbs) such as leg replacements. This new prosthetic will be able to be controlled with a human mind. It will certainly be a breadthrough when the study is final, but it will take five years to complete.
I beleive that prayers help your mental disposition in a way to cope with ill health...but it won't perform a healing miracle. Remember that the Apostle Paul had poor eyesight, and prayed to have his vision improved. He didn't get that prayer answered.