This YouTube video ("The Truth About Vaccine Testing") features a speaker arguing that while vaccines undergo safety testing and placebo-controlled trials, many trials used active placebos rather than inert placebos (e.g., saline). The speaker notes older vaccines were sometimes tested using less rigorous methods decades ago and suggests that comparing vaccines against inert placebos might reveal different safety signals.
Chapters
A lot of vaccines have not gone through extensive rigorous testing at the level that other drugs and treatments and modalities have gone through. Almost none of them have. So you have to be very specific because people twist and turn this. They have gone through a lot of safety testing before they hit the market. It's not like they haven't done that. They have done placebo controlled trials. Absolutely have. They haven't done inert placebo controlled trials. There is a big difference because the vast majority of the research when it comes to vaccines has been studied against an active placebo. And the first vaccine wasn't studied in the best way because it was maybe done 20, 30, 40 years ago. So it wasn't to the level that we did now. So you're saying something is safe based on something else, and it's not against nothing, but if you did it against an inert placebo like saltwater, you might actually see a difference there and maybe there is some sort of danger that you need to be concerned about.