The article actually _does_ mention challenges to the real virus, at the end of the "What are the next steps in the trial?" section: > There are also calls to

The article actually _does_ mention challenges to the real virus, at the end of the "What are the next steps in the trial?" section: > There are also calls to perform "challenge trials"[1] in which vaccinated people are deliberately infected with coronavirus. However, there are ethical concerns due to a lack of treatments. [1] https://www.bbc.com/news/health-53426367 https://www.bbc.com/news/health-53426367