Letter from Colin M. MacLeod to United States Army, Office of the Surgeon General

During World War II Heidelberger developed a simple vaccine against pneumococcal pneumonia, like other infectious diseases a serious health threat among soldiers. The Pneumonia Commission of the Board for the Investigation and Control of Influenza and Other Infectious Diseases within the Office of the Surgeon General of the U.S. Army, headed by Colin MacLeod, a microbiologist and co-discoverer of the genetic properties of DNA, organized a trial of the vaccine in 1944, as described in this memorandum. The trial, carried out among 20,000 trainees at an air base in Sioux Falls, South Dakota, proved that a vaccine made from a mixture of purified capsular polysaccharides from four different types of pneumococcus was effective against the disease.