Prevention depends on the cause. For example, avoiding strenuous activity can prevent shortness of breath. Regular exercise can get people in shape so they're less likely to get short of breath with normal activity. Many cases of shortness of breath from asthma, congestive heart failure, and panic disorders can be prevented by taking medications regularly. Many cases cannot be prevented.
Long-term effects are related to the cause. For example, shortness of breath due to exercise has no long-term effects and is usually encouraged. Pneumonia treated with antibiotics often goes away and causes no long-term effects. Shortness of breath due to lung cancer may result in death. Heart attacks and congestive heart failure may cause serious disability and limit a person's ability to perform normal activities.
Most causes of shortness of breath are not contagious and pose no risk to others. But if the cause is an infection like pneumonia, it may be contagious.