The Prayer of Faith in James 5:14-15

James 5:14-15 says to us,

“Is anyone among you sick?  Then he must call for the elders of the church and they are to pray over him, anointing him with oil in the name of the Lord; and the prayer offered in faith will restore the one who is sick, and the Lord will raise him up, and if he has committed sins, they will be forgiven him.” 

What is the level of faith that is required to be healed according to this? 

If we have faith enough to believe He is able to do it, I think that this is sufficient,

“As Jesus went on from there, two blind men followed Him, crying out, ‘Have mercy on us, Son of David!’  When He entered the house, the blind men came up to Him, and Jesus said to them, ‘Do you believe that I am able to do this?’  They said to Him, ‘Yes, Lord.’  Then He touched their eyes, saying, ‘It shall be done to you according to your faith,’ Matthew 9:27-29.