Ok, I actually did some research on WC and immunisations myself. Canada has the worst rate of WC in the more developed countries... and they have taken a strategy of giving the mother a booster after labour. It takes 10 days for the antibodies to go through to the breastmilk - which gives babies passive protection from Whooping Cough until their first needles.

NSW Health also informed me that the youngest you can take them for immunisation is 6 weeks.