Ex 15:26 – And said , if thou wilt diligently hearken to the voice of the LORD THY God, and wilt do that which is right in his sight ,and wilt give ear to his commandments , and keep all his statutes , I will put none of this diseases upon thee , which I have put on the Egyptians I am the LORD  that healeth thee.

The healing covenant is conditional , and the condition of course is to live right before God.