I agree with this. You can ask, but that is all you can do. You cannot expect them to actually do it. And if they don't you need to respect that.
And in return they should respect that they won't be able to visit the baby. I would simply let people know now (and in light of what happened to your friend's baby I think your concerns are reasonable) and they can choose what they want to do. FWIW we had a whooping cough outbreak locally and I saw first hand 2 children and an adult deal with it. I had the booster as there was no way I wanted myself or my girls to go through that!