Simplify the following text for a Grade 9 native English-speaking person.
Original: The III-S strain covers itself with a polysaccharide capsule that protects it from the host 's immune system , resulting in the death of the host , while the II-R strain does n't have that protective capsule and is defeated by the host 's immune system .
Simplified: The III-S strain covers itself with a polysaccharide capsule that protects it from the host 's immune system .