On the basis of the problem of the possible compulsory nature of vaccines against Covid-19, this paper considers the sources that allow us to justify the imposition of collective measures. The social contract theory provides a rational basis for the universality of ethical and natural law obligations, including conditional respect for a protected domain of individual physical and moral integrity. However, the practical application of the covenant is subject to the uncertainty of what effective consequences the policies have. Ethical principles (...) show the problem of application in the environment of epistemological uncertainty. Only in a free society, with free scrutiny and deliberation, can justified knowledge be achieved that allows social measures to be agreed upon. The characteristics of the case that is the subject of this article lead to the conclusion that Covid-19 vaccines are not ethically obligatory, universally, but they can generate reasoned health measures, promotion, and limitations, based on proven positive effects, as a technical matter. (shrink)