In part 1 I briefly looked at the reason for writing the series and one possible reason that someone might choose to forgo vaccines for himself or his children. Please note that I am neither pro- nor anti- vaccine, but instead believe in researching and deciding what is best for that person in that situation. I feel that people should have the right to decline or choose any medical procedure or medicine, though I feel all such decisions should be undertaken after looking at all the pros and cons using reliable information. I am not a medical professional and would never presume to give medical advice; I am merely exploring the various reasons one might have for refusing some or all vaccines.
I'd think a major reason would be if the parent or child has had a serious adverse reaction to a vaccine. As with any medicine, adverse reactions of varying severity are possible, even if not common. Obviously if it is serious, then the vaccine insert itself states that the vaccine shouldn't be repeated, or at least that is the case for the DTaP vaccine (note that this is actually the one given in the UK, so it may be different for the ones given in the US; a more complete listing for reactions to the vaccines in the US is found on the CDC website), which is the one I've looked at most. For reactions that aren't quite as serious, then the risks and benefits should be weighed very carefully (the risks and benefits should be weighed regardless, in my opinion, but the analysis does change once an adverse reaction has been observed). The majority of adverse reactions are milder, though as with any medicine or disease, the possibility exists for a more serious reaction in some cases. Nothing is risk-free, though: whether one vaccinates or not, there are risks. Some may find the risk of vaccination unacceptable at any time, some may find it unacceptable after a more serious adverse reaction, and some may find the risk of the disease outweighs the risk of the vaccine at any time. I do not think any of those decisions is wrong, nor are any necessarily uneducated decisions.
On a similar note, some may forgo vaccines based on allergies or intolerances to other ingredients in the vaccine. The most common warning is given to those who have severe egg allergies, as some vaccines, such as the one for influenza, are created using eggs. For many, this doesn't present a problem, but for some this would warrant skipping the vaccine. Less discussed is that some vaccines contain bovine proteins, which can present a problem for those who have an intolerance to such proteins. I've no idea how often that would present a problem, so the person in question would have to evaluate whether the risk of reaction was high enough to warrant avoiding the vaccine. I would imagine such reactions are rarer, just as an infant with a dairy intolerance can often tolerate the mother consuming dairy; I do know from personal experience with Charlotte, though, that there are at least some infants who cannot tolerate that and have the same reaction to a vaccine with those bovine proteins. In the case of an intolerance, which may sometimes be outgrown, some may choose to simply delay the vaccine until the intolerance is no longer an issue, as well. Again, I don't see any of these options as wrong, and I cannot presume to say what a particular person should or should not do medically-speaking.