Vaccine control types recap👇 🔹 Placebo: saline/inert when no licensed vax exists. 🔹 Active comp: Gardasil vs alum-only (blinded); PCV13 vs Prevnar. 🔹 No-intervention: early trials just observed unvaxed (pertussis ’34–38, Salk ’55). 103 trials·1.79 M pts www.bradspellberg.com/vaccine-rcts