The vaccine isn't 100% effective, like others have said, but it lessens the severity of pertussis. I find the information about Australia interesting, because I've wondered if just lessening the severity of the illness for a person would keep an infant from getting it. That said, my husband is due for a tetanus booster and is considering getting the TdaP (the adult version of the DTaP) since he hasn't had it and we'll have a newbie in the winter.
I personally think the best option is to stay home with your newborn, and try and minimize situations where exposure would be a problem. I know it's hard if there are older children in daycare/school and I even worry about my husband bringing it home from the office. But I think if you stay home with your newborn, breastfeed, and you eat well then you're not likely to have your child pick up pertussis.