In May 2020, the biotechnology company Novavax began human trials of its Covid-19 vaccine. The Phase I trial was a placebo-controlled, observer-blinded design. Most clinical trials go through five phases: Phase 0 (Pre-clinical), Phase I (Safety), Phase II (Efficacy), Phase III (Comparison), and Phase IV (Surveillance). Research the five phases of a clinical trial. Discuss the ethics involved in using control groups for a potential life-saving vaccine.