Vaccines have been an important part of modern medicine, used as a preventive tool to protect us from disease like polio, tetanus, or small pox. These vaccines work by challenging one’s immune system with an inactive agent similar to the real pathogen. Thus, when faced with the real disease agent our body is able to effectively and efficiently mount an offensive to prevent illness. However a new study is showing that despite vaccines, pneumonia hospital visits still remain quite common. Here's why.