Authors from the National Institutes of Health (NIH) and colleagues suggest ways in which we could learn by continuing to follow vaccine trial participants who originally received placebo. They mathematically demonstrate that long-term placebo-controlled vaccine efficacy can be estimated even after the placebo group has been vaccinated. While less precise than estimates from a standard trial where the placebo group remains unvaccinated, this proposed approach permits assessment of the durability of vaccine efficacy and whether the vaccine eventually becomes harmful to some.
