Praying when you know you are being prayed for has an effect, but similar to the effect of "positive thinking."
All studies that have been *well designed, placebo controlled, double blinded RCTs* have shown no effect, or have not been replicated, or have not been sufficiently "powered." All studies that have shown an effect had one or more defects. Mainstream science has shown no effect of remote prayer.
I'm not saing anything about religion, or the personal benefits of prayer, spirituality, positive thinking, etc. But *scientifically* there is no proven effect of remote prayer. I'm a science guy and looked into this a few years ago so unless there have been major new developments (which I doubt) this is not considered an area of serious science/medicine.
Now positive thinking, positive social support structures, personal beliefs and coping strategies, even number and depth of friendships - - - these HAVE all been shown to have beneficial health effects.