As a frontline, Viktor's Barrage will be blocked by your shield if the center of the blast is outside your shield. The missiles are just a visual effect, and the explosions actually spawn at ground level.
If you pressure Seris into using her escape, turn around and listen for Seris uncloaking. Try getting someone low in the mean time, this will often cause Seris to believe she is safe since you aren't looking at her and will uncloak to heal her team.