This phrase expresses a situation that started when something happened, and then continues until the present. In the example above, the situation is that there's an open position. The event that happened was that Vicky left the job.

The event should be the cause of the situation. For example:

Now that he's retired, my dad can spend a lot more time working on his garden.

The speaker's dad's retirement is the reason that he can spend more time working on the garden.

If the situation isn't related to the event, use "since (something happened)":

My dad's been having trouble sleeping since he retired.

In this sentence, the speaker's dad's sleep problems aren't related to his retirement; they just started happening in the time period after he retired.