Sportal.co.nz 27.Feb.2013Getty Images
Successive defeats to Italy, Wales and England have left Les Blues battling to avoid the wooden spoon and Saint-Andre has brought in Medard for Racing Metro's Benjamin Fall and Vahaamahina for Toulon's Jocelino Suta.
Saturday's 23-13 defeat to England at Twickenham followed losses against Italy and Wales, but Saint-Andre has opted against wholesale changes, instead only making a couple of tweaks to his 23-man selection.
Medard has not played for France since last year's Six Nations, while Vahaamahina has just one cap to his name, which came against Australia in November.
Saint-Andre said: "We have made these changes on the basis of our performance against England.
"We worked much better as a team at Twickenham and we need to build on those improvements.
"When you have a lot of players who are learning the high level of the international game, this continuity is important."
Saint-Andre revealed he had been following both players for some time and he received good reports about their club form.
"We looked at all league games this weekend and revised our end game," Saint-Andre told reporters.
Medard's return from injury had shown he was ready to join the national team set-up.
"Maxime (Medard) showed that after his injury he returned to his best and he will bring his qualities and experience."
The France coach has also been impressed by the way Vahaamahina has built on his single cap by continuing his good form at Perpignan.
"Sebastien (Vahaamahina) participated in the November matches with Team France.
"Currently he is very successful with his club, he is young and has a margin of interesting progression for the France team."
Saint-Andre has also earmarked both players as being in contention for the France squad for the 2015 World Cup which will be staged in England.
He added: "They are players that we have followed for a long time for the World Cup 2015, they have returned to the group and they can work with the community and gain playing time."