evidence: COVID-19 Vaccines: Verifying Safety and Identifying Misinformation How do we know COVID-19 vaccines are safe? [...] GG: There are different phases of conducting a clinical trial. I referred to these vaccines as being in phase 3 trials. This is the last phase where people are looking at safety and efficacy. The first phase is purely [for] safety. It's [tested on] a small group of people to make sure that the vaccine [is] well tolerated. And in the second phase, they get a little bit more into the safety part and what kind of doses are required.