Table 2.

Illustrative Quotes for Themes and Subthemes.

Theme	Subthemes	No.	Quote
Vaccine safety	Vaccine quality and contents	1	“‘I’ve done all of my research and there are all of these chemicals and this specific chemical,’ I don’t even know which chemical they are talking about. . .they worry about those kinds of things.” (WA FG 1, Participant 4)
		2	“‘Well the flu vaccine isn’t very good.’” (CO FG 1, Participant 14)
		3	“‘Oh, I’m concerned about the additives.’” (SSI 3, Participant 20)
	Health-related consequences	4	“. . .I have odd resistance to HPV vaccines from parents because of some vague complications and rumors that they heard about what has happened in Australia which I asked one mom to send me the information because I have heard it now from multiple places although I’ve never heard of what the chronic fatigue issues, rheumatologic issues. . .those are the sorts of things I have heard.” (WA FG 1, Participant 2)
		5	“Yeah, they’re still there that [vaccination] causes developmental issues.” (SSI4, Participant 21)
		6	“‘It’s causing autoimmune diseases in late adolescence and adulthood.’” (SSI 4, Participant 21)
	Unnatural/overwhelming for body	7	“And [his] mom asked me, ‘isn’t this going to be too much for his body to handle? Putting all of this in?’” (CO FG 1, Participant 15)
		8	“‘It just seems like a lot, isn’t it just too much, I want to give their immune systems time to develop.’” (CO FG 1, Participant 17)
		9	“‘. . .it’s not natural and we were fine without them.’” (WA FG 1, Participant 5)
		10	“. . .the concern about overwhelming the immune system and that doesn’t feel right to them.” WA FG 1, Participant 5)
		11	“‘. . .don’t believe that these chemicals are appropriate for our child.’” (WA FG 1, Participant 5)
	Incomplete/inadequate data	12	“. . .but I feel like a lot of people told me lately that there’s been no studies, or only short studies on safety of vaccines.” (CO FG 2, Participant 27)
		13	“‘This vaccine hasn’t been studied in people like me.’” (WA FG 2, Participant 32)
		14	“‘. . .we’re not getting anywhere with this until I research this more and I want you to pull out specific data.’” (WA FG 2, Participant 30)
Relative influence of information sources, decision-makers, and timing	Parent claims to have all the information needed for decision to refuse/delay	15	“[Parent] said ‘I’ve done my research, I don’t want anyone to talk to me about shots. Don’t bring up the subject.’” (WA FG 1, Participant 6)
		16	“. . .the ones who say ‘I know a lot, I’ve read a lot.’ And they won’t tell you what they’ve read or know. And you’re stuck.” (CO FG 1, Participant 12)
		17	“. . .where the mother does not want to make the decision without the husband there. . .” (WA FG 1, Participant 4)
	Need to consult family member who isn’t present	18	“So sometimes I hear, ‘well I can’t make this decision without my husband’ for instance.” (WA FG 1, Participant 1)
		19	“‘I need to talk to my husband. . .’” (CO FG 1, Participant 17)
		20	“. . .where the mother does not want to make the decision without the husband there. . .” (WA FG 1, Participant 4)
	Parental promise and convenience	21	“‘I promised him no shots today.’” (CO FG 1, Participant 17)
		22	“The one I’ve been getting recently is ‘oh we’re going on vacation, so we’d rather wait. We don’t want them to be fussy.’” (CO FG 2, Participant 27)
		23	“‘We have a plane trip tomorrow, I cannot deal with that.’” (CO FG 2, Participant 27)
	Discordance	24	“Usually it’s the mom saying ‘I’m not getting it because dad doesn’t want it but dad won’t come in and talk to you.’” (WA FG 2, Participant 30)
		25	“I had a dad the other day hold up a sheet of paper that had the questions that his wife had written out for him. And at the bottom in capitals it said, ‘No HPV, No Immunizations.’ And he’s like, ‘See?’ I’m like, ‘I’m not going there today. I’ll talk to mom next time.’” (CO FG 1, Participant 14)
Low perceived risk of contracting VPD	Due to limited exposure to susceptibility factors	26	“. . .parents that say, ‘my child’s not going to be exposed much because they’re in a daycare of this size.’” (CO FG 1, Participant 12)
		27	“I feel that there are religious families that see it as more for promiscuous kids.” (WA FG 1, Participant 3)
		28	“I think a lot of families think that they can only get it (HPV infection) from like sex.” (WA FG 1, Participant 2)
	Due to proximity to outbreak	29	“I’ve asked [parents] what their thoughts were about the outbreak. . .many of them seemed like they’d already talked it through. . . and had come to some narrative about based on where they live that it was unlikely their child would be exposed.” (SSI 2, Participant 19)
	Differential risks among VPDs	30	“. . .when measles hit Disneyland, there was an uptick in people who wanted their measles vaccine. Pertussis never seems to do it. I spend a lot of time telling people ‘yes there is pertussis, yes there is pertussis.’” (CO FG 1, Participant 17)
		31	“Mom only insisted on one vaccine. Wants to talk with provider. What is the most important one?’” (SSI 1, Participant 18)
Lack of trust	Lack of established relationship with provider	32	“. . .at 2 months and you don’t have the rapport with them and they decline for whatever reason.” (WA FG 1, Participant 4)
		33	“I think one of the things is that we start vaccinating at 2 months and if they are not an established family and have not done a meet and great with you and they have seen 1 or 2 other people you don’t have the street cred that you might have later.” (WA FG 1, Participant 3)
	Government mis-/distrust	34	“. . .they often mum the reason because I think it’s more of a government mistrust thing.” (WA FG 2, Participant 31)
		35	“. . .it could be that for the African families, similar to the eastern European families, depended on government distrust.” (WA FG 2, Participant 31)
Religious objection	Usage of porcine products	36	“. . .far more refusal from patients presenting as Muslim and saying. . .that it is because it has pork. . .” (WA FG 1, Participant 1)
		37	Moderator: “. . .And the gelatin among Muslim families. . .” Participant: “Yeah. So that’s something we hear from time to time. . .” (SSI 4, Participant 21)
	Usage of aborted fetal cells	38	“I think I have a hard time with like the silly concerns. The aborted fetal cells, like the ones where I guess I just need to do more research.” (CO FG 2, Participant 27)
		39	“You know or like the super right-wing Christians, born from aborted-fetal cells.” (WA FG 2, Participant 29)