Investigators in the Division of Infectious Diseases and the Division of Hospital Medicine of The George Washington University Medical Center are carrying out a study to determine if hospitalized patients receiving the polyvalent pneumococcal vaccine during an acute illness develop an adequate antibody response. The study group will consist of individuals diagnosed with pneumonia and admitted to the Medicine ward under the Pneumonia Core Measure Protocol, which assigns appropriate patients for vaccination based on the current guidelines from the Advisory Committee on Immunization Practices (ACIP).