( 1 ) Positive rate of blocking antibodies : the positive rate of blocking antibodies were 17 % ( 4/23 ) , 58 % ( 42/73 ) , 72 % ( 53/74 ) and 84 % ( 76/90 ) in the 2 , 3 , 4 , and 5 times of intradermal injection group , respectively ( P < 0.05 ) .