Thanks to an impressive R&D effort, three vaccines for Covid-19 have been conditionally approved by stringent regulators as of February 2021, and sixteen have entered the WHO evaluation process. However, they all need to keep on being evaluated in clinical trials. The WHO Ad Hoc Expert Group on the Next Steps for Covid-19 Vaccine suggested that countries with limited or no access to an effective vaccine could ethically permit placebo-controlled trials, even if effective vaccines were already being marketed elsewhere. Here, I argue that inclusion in a placebo-controlled trial is ethically sound for those who would be in any case ineligible for vaccination outside the trial, and as long as the access to the vaccine outside the trial depends on a transparent and just allocation framework. Conversely, carrying out placebo-controlled studies in countries where vaccines are not (or are insufficiently) available because of unequal global allocation, would be unethical, as an ethical strategy cannot be built on an unethical premise.