evidence: Double-blind randomized controlled trials (RCTs) became mandatory for FDA approval of new medications around 1980. This is still a discipline in evolution. As it turns out, blindness breach is rife, although seldom consciously apparent. Shapiro et al. found in a meta-analysis that at the end of double-blind RCTs, treatment assumptions (TAs) were correct in 72-100% of cases [1]. TAs are subjects’ intuitive guesses of group allocation to the verum or placebo group. Nevertheless, reporting upon the success of blinding is uncommon. We didn’t find any in vaccination trials. [...] The two studies compare a verum to a passive placebo (injecting 0.9% sodium chloride solution). Compared to an active placebo, a passive placebo can have fewer adverse events. In the case of RNA vaccines, using a passive placebo causes a risk of a breach in blinding, given the consciously and non-consciously felt adverse events of the verum, potentially heightening the "placebo effect" in the verum study arm. This may be of particular concern here because measuring efficacy is based on patient-reported symptoms. In both studies, nonblinded administrators further risk diminishing the double-blind through non-conscious communication. [...] TA data can be used to improve the scientific validity, and indicate whether an active placebo is needed. Assessing TAs is interesting for vaccine producers. They are relatively low-cost additions that make trials more efficient.