Poliomyelitis leading to large-scale trials in the then Belgian Congo and the vaccination of seven million children in Poland against serotypes PV1 and PV3 between 1958 and 1960. The second inactivated polio virus vaccine was developed in 1952 by Jonas Salk at the University of Pittsburgh, and announced to the world on 12 April 1955. The Salk vaccine, or inactivated poliovirus vaccine, is based on poliovirus grown in a type of monkey kidney tissue culture (vero cell line), which is chemically inactivated with formalin. After two doses of inactivated poliovirus vaccine (given by injection), 90 percent or more of individuals develop
Salk of soldiers (fire and maneuver team) forming a fireteam. Salk A salk () is a small military unit led by a senior soldier that is subordinate to an infantry squad. "Salk" is bigger than a lahingpaar ("fire and maneuver team") but smaller than a jagu ("squad"). It is also one of the smallest military formation among the Estonian Ground Force infantry units. It usually consists of three to five soldiers, and may be further subdivided into fire and maneuver teams. A "salk" is composed of two fire and maneuver teams of two soldiers each, as well as a fireteam leader