A total of 6145 children were randomly assigned at a ratio of 1:1:1 to receive 2 injections 21 days apart of A/California/7 / 2009 ( H1N1 ) - AS03 vaccine at dose 1 and saline placebo at dose 2 , 2 doses 21 days apart of A/California/7 / 2009 ( H1N1 ) - AS03 vaccine ( the Ad2 group ) , or 2 doses 21 days apart of nonadjuvanted A/California/7 / 2009 ( H1N1 ) vaccine ( the NAd2 group ) .