差分

 *duration of activity VDPV is relatively physically stable in environment/sewage - seeding period but cannot keep infectivity not for long time, thus continuous detection of years VDPV in enviromnent means duration of activity of each virus continuous transmission and/or continuous producing excretion of VDPV due to OPV *how to keep activity from people living in environment/sewage - can the virus propagate in some cells in sewagecommunity*any intervention directly to sewage where VDPV has been found, like distribution of breech (disinfectant*where the sabin virus obtains mutation to ) and/or irradication ultraviolet light may be effective against PV/VDPV*threshold of immunization coverage to maintain PV/VDPV freeis 85-90%