They don't do the 18mth vacc now - he wouldn't need any until 4yo now unless you wanted him to have the chicken pox vacc which is given at 18mths. And yes you can choose to stop vacc even if you have started them. You will still need to get a letter stating that you are a conciencious objector for when you enroll in preschool etc. This also wont affect you getting the maternity immunisation payment either as his vaccinations are currently up to date at this point in time.