Table 1.

Negative, hesitant, and ambivalent claims posted by Facebook users on Facebook advertisements categorized by themes (n=130).

Themes		n (%)	Examples of claims within comments
Contextual influences		19 (14.6)
	Mistrust in pharmaceutical industry or government transparency	18 (13.8)	Pharma wanna make money...Bottom line is that vaccination is all about $$$$$... The chances of your child dying from these diseases is highly unlikely. There is SO much gov involvement...
	Religious values	1 (0.8)	I come from a Mennonite background where we were not vaccinated.
Individual and group influences		85 (65.4)
	Lack of knowledge or awareness (misinformation and belief in own knowledge or research)	27 (20.8)	Lmao the courts admitted to vaccines causing autism...But they did it quietly! If I find the article I will post it on here...I do not vaccinate my children and never will...liquid mercury is metal you are injecting into your children... The argument that an epidemic would break out if children were not vaccinated is proven incorrect by every Amish/Mennonite community that is thriving today. Recent studies have shown startling evidence that links autism directly to vaccines along with decreased brain function. If you would like sources to this I can provide them. All sorts of diseases have been directly linked to vaccines including and especially autism...I hope wise people everywhere choose to educate themselves before making this decision. From my observations, limited as they are, the immunized ones tend to be the ones lacking basic immunity.
	Risk or benefit of vaccination (perceived, heuristic)	23 (17.7)	...so in my opinion he still would have a chance of getting these illnesses if I vaccinated him so I don’t see the point in giving him something that WILL harm him for a CHANCE that he might not get sick...There are some vaccinations that (my) children will not get (like chicken pox) as I think it is an unnecessary risk... There is absolutely no protection from a disease from taking a vaccine! But there are many people who die from vaccines every year! Don’t fool yourself. EVERY TIME you vaccinate there is a risk, even of death. It is up to you to decide if that risk is what is right for your child. For some children it might be worth it, but for other children it isn’t worth it...There are risks and there are children that are much better off without vaccines.
	Health system and providers (trust and personal experience)	15 (11.5)	Ask your doctor?! No Doctor is God. They are all trained to say the same thing. The truth is none of us know the truth. Any health care professional will side with pro vaccine idea. I will not vaccinate my son. Do you even know what your injecting in your kid?
	Beliefs and attitudes about health and prevention	10 (7.7)	My children have needed to see a doc approximately never in their lives. They are a testament to a holistic lifestyle and natural immunity. My observations of most kids that have been vaccinated is that they seem to be endlessly ill and have had multiple courses of antibiotics in their short lives!!
	Experience with past vaccination	10 (7.7)	My son had convulsions after getting vaccinated, that was 19 years ago and no vaccines again.
Vaccination or vaccination-specific issues		5 (3.8)
	Role of health care professionals	3 (2.3)	...my paediatrician & general practitioner both disagree with vaccinating...
	Vaccination schedule	2 (1.5)	None of this 3 in 1...Dangerous injecting 2-4 shots in a kid at one time...
Other		21 (16.2)
	Parents’ right to choose and not be judged	18 (13.8)	I think every parent has the right to chose what is best for their child. I don’t think it’s right for other parents or people to judge others for what they decide!!! I find it incredibly interesting that so many people are bothered by someone else’s choice to vaccinate or not vaccinate. If you get vaccinated, who cares if someone else doesn’t, it’s not your life....Everyone needs to take a chill pill... Defend your vaccines all you want but don’t call us idiots for not taking them!
	Requesting information or sources	3 (2.3)	Do you have any sources for your input?