Pneumonia can occur at any age. However, it is most common in the elderly and children. Some have a higher risk of developing pneumonia because of the presence of other lung diseases, malnutrition, swallowing difficulties, other chronic health problems or immune system problems. People who smoke and are in a smoking environment are also at higher risk of developing pneumonia. In addition, people who do not have an annual flu vaccination, or who are vaccinated with Streptococcus pneumoniae vaccine, also have a higher risk of lung infections.