Simplify the following text for a Grade 11 native English-speaking person.
Original: Low-risk disease is most common in infants and good outcomes are common with observation only or surgery , whereas high-risk disease is difficult to treat successfully even with the most intensive multi-modal therapies available .
Simplified: Low-risk disease is most common in infants and good outcomes are common with observation only or surgery . High-risk disease is difficult to treat successfully even with the most intensive multi-modal therapies available .