How do they know that your baby will build antibodies and immunities from the H1N1 vaccination?

If there have been no studies on newborns whose mothers have gotten vaccinated considering this vaccination just came out? How is their proof that your baby will be protected from the swine flu? Maybe this is a dumb question, but I just don't get it. It's sounds like an educated guess to me or something to hype up the shot to make it sound more appealing to pregnant women.