There are currently more than 750 such areas in the National Wilderness Preservation System comprising over 109 million acres -- roughly 5% of the United States by area. Need a refresher from the other 95%? The Active Times picked 10 wild places in the lower 48 states that are truly wild.
Polio, which struck children disproportionately, could attack the central nervous system and cause muscle deterioration, paralysis and even death. American virologist Jonas Salk, who was born 100 years today on October 28, 1914, developed the worldâs first safe and effective polio vaccine.
Both the Salk and Sabin vaccines are âtrivalentâ that is, active against all three virus types. Type 2 poliovirus has not been detected anywhere in the world since 1999. A person who gets polio is immune to future infection from the virus type that caused the polio. Poliovirus bound to a neuron receptor Illustration courtesy of Link Studio. Scientifically accurate bronze models (without patina) of the poliovirus created for the Smithsonian by Edgar Meyer, 2005.