as long as your GP is the one putting the needles off, he can send through an approved catch up schedule to ACIR and they won't hassle you about being late as the doctor has notified that s/he is aware and is working with you (well, that's the information we've been given at work anyway!)

with chicken pox, i dont think it is compulsory yet - it's a one off needle and i haven't heard anything about it being compulsory yet