Illustration of a polio virus particle binding to the CD155 receptor on a human cell (bottom). Each virus consists of a protein coat (capsid) surrounding a core of RNA (ribonucleic acid) genetic material. Poliovirus infects children causing the disease poliomyelitis, or infantile paralysis. Although it normally only causes a mild illness, in some cases it infects the central nervous system (CNS) and can cause severe damage, leading to paralysis or death. Vaccination, which started in the 1950s, has been successful in controlling the disease.