evidence: If, at the recommendation of a friend, you decided to "do your own research" on the topic, I understand the resulting confusion. The World Health Organization had to convene an expert panel on the issue of placebos in vaccine trials after acknowledging that guidance documents from different international bodies were conflicting. This is because vaccines don’t exist in a vacuum: their circumstances help dictate the kind of control they should be pitted against. A vaccine can be the first of its kind against a disease or it may be a challenger to the throne. It may immunize against more strains than a preexisting vaccine or it may be identical to a vaccine on the market except for the addition of a special molecule meant to boost the immune reaction. A saline injection may be an ethically valid control in some of these instances but not in others. [...] This being said, there is a persistent argument online that contaminates minds like a bad virus: that no vaccine has ever been compared to a saline solution. This is simply untrue. The website Virology Down Under lists specific trials of important vaccines that were placebo-controlled and this article from the Vaccines Work Blog specifically lists a number of saline placebo vaccine studies.