Prevention is related to the cause. Avoidance of stress and overexertion, getting enough sleep, and eating a healthy diet can prevent some cases of malaise. Taking medications as prescribed can prevent some cases due to diabetes and allergies.
Malaise can limit a person's ability to work or go to school. Other long-term effects depend on the cause. For instance, cancer may result in death. An infection often goes away and results in no long-term effects.
Malaise itself is not contagious and poses no risk to others. However, malaise may be caused by an infection that is contagious.