The reason vaccines are compared to non-saline is because, when testing a vaccine one must test it where the disease occurs, or you can't tell if it prevents any cases, so that has often meant a developing country, the leaders of which then ask why *their* children are used as lab rats but get no benefit from the study, since they can't afford to buy the vaccine once it's on the market. So human subjects research ethics requirements are that all study subjects should get a benefit of some sort from being in the study, but the incentive can't be so great as to have the effect of pressuring people who otherwise would not volunteer, because it would be too much like forcing their participation (and, yes, I know that millions have been forced into the covid injections, and that has been one of the stunning aspects of the whole fiasco). One way this issue has been handled is to give, e.g., Hepatitis B vaccine as the comparator for a Hepatitis A vaccine trial. There should be no effect on incidence of Hepatitis A in the Hep B vaccine group, and the Hep B group would get the benefit of being protected from Hep B (you don't have to agree with the level of protection, just know that that is the rationale). Safety is mostly addressed in Phase I, not the big Phase III clinical trials, but I believe that drug and vaccine manufacturers have begun (or perhaps I just recently noticed) to rely on "post-marketing surveillance" to find less obvious health risks. That simply means they put the product on the market and see who keels over (and they're not doing this to standard for the covid injections, either). Ideally, the comparator vaccine has all of the same contents as the intervention/test subject vaccine, so the only effect of the intervention should be to either prevent the disease or not; it clarifies comparisons. That too weighs against using saline. A trial for adjuvant and other contents would compare injection with those constituents, ideally separately, with saline, but I don't think there's enough economic incentive to do that, since many of the constituents are accepted as 'normal' (including who knows what in the covid injections, of course - the whole thing has so disappointed we who took all those certifications in human subjects research protections and whose scientific careers would have been quickly ended had we done 1 zillionth of what has been done) and, importantly, they aren't patentable, which is what provides the profit in drugs and vaccines. (I too had all of what used to be called in medicine the "usual childhood diseases," which came with its own handy abbreviation for patient notes, UCHD, and I too have become a vaccine skeptic. I too am old, and I may have had my last vaccine ever.)