After receiving a birth dose of trivalent OPV , we enrolled and randomly assigned newborn babies ( @:@:@:@ ) to receive two doses of mOPV@ with an interval of @ week ( mOPV@-@ week ) , @ weeks ( mOPV@-@ weeks ) , or @ weeks ( mOPV@-@ weeks ) between doses , or two doses of bivalent OPV ( bOPV ) with an interval of @ weeks between doses ( bOPV-@ weeks ) .