Vaccines preventing Covid-19 have been approved in several countries. Is it still ethically acceptable to use placebo controls during the development of other vaccine options? If two of the most influential international guidelines of biomedical research are consulted, the Declaration of Helsinki and the CIOMS-guidelines, the answer is "no". We discuss the implications for ongoing vaccine research, and how placebo controls might be justified nevertheless. However, the ethical conflict remains highly problematic. We suggest that such ethical dilemmas should be avoided in the future by the introduction of a new system of global governance. Once vaccines are approved, a global regulation should oblige producers to provide the necessary amount of vaccine doses for the control groups of ongoing vaccine research.