just thought of something - with the older vaccinations the first one gave most people immunity but later ones ensured a higher coverage. Don't know enough about the 5 in 1 to know if that is the case but it might be worth asking if you could have a blood test done to check your child's level of immunity.
Hope your dh can visit his dad - he'll regret it later if he doesn't manage to go but a lot of men are so useless about knowing what to say and do.