So the Creator of all is incapable of protecting His Own from sickness?This is true. There are also those with a suppressed immunity system due to disease to start with and not a matter of keeping their immune system in shape. Seems that genetics plays a key role in the strength and effectiveness of one's immune system and not so much a matter of faith or of one's regimen in keeping it in shape.
https://www.hopkinsmedicine.org/health/conditions-and-diseases/the-immune-system