No, it won't be asymmetrical. You decrease one on each side of the vest back on every row you work decreases.
You decrease 1 at each end of every row, 1 at the beginning and 1 at the end for (Sue did the math to determine) 5 rows. Put another way, decrease 1 on the right then decrease 1 on the left side of the piece you're working on. (Left and right respective of how you are looking at it)
Then, every other row (alt rows) you decrease 1 at the beginning and 1 at the end of the row till your stitch count is 79.
ETA: Oops! I just saw your last post. You were talking about asymmetrical so I thought you were confused about dec. on each end. Sorry.