Very confident. If the question was do you have doubts about the efficacy of vaccines the answer would be yes.
These surveys make me uncomfortable. I respect the 2 to 4% who refuse to respond. When the statement is "The Earth is 4.5 billion years old," what is the alternative? 4.6 billion years? 4.54 billion years? Six thousand years? I think you are expected to turn off most of your critical thinking and say "yeah, sure, everybody knows smoking causes cancer" (4% not too/not at all confident).Very confident.
You're one of the good guys then. The article worries about those who were "not too confident" (11%) or "not at all confident" (4%), saying that "15 percent — have doubts about the safety and efficacy of childhood vaccines." PDF with results.