Polio research. Dr Li and Dr Shaffer conducting polio research in a laboratory. The polio virus causes the disease poliomyelitis, or infantile paralysis. In severe cases the virus infects the central nervous system (CNS) causing inflammation and nerve cell death. This causes muscle weakness in the muscles served by the nerves and can lead to paralysis. Vaccination, which started in the 1950s, has successfully controlled the disease. It has now been eliminated in Europe. Photographed in Montgomery, Alabama, USA in 1953.