2) Can you speed up the testing process with challenge studies, where volunteers willingly get infected?

It’s a great question and I applaud the people who ask it and I applaud those signing up to do it. I’m not sure I am a huge fan, for both practical and ethical reasons. The devil is in the details. A challenge study has to show us a vaccine can prevent not just infection but prevent disease. Otherwise, how do I know the dose in the challenge study is the right dose? If you take 100 young people, 90 of them will get mild or no disease. Ten may end up in hospital and one in the ICU.

Also, the timeline. Can it let you skip Phase II of large efficacy trial? The reality for us is that we are about to start Phase II anyway. It would be months before a challenge trial could be designed. And ethically: everybody agrees there is a risk that is not zero of having very serious disease. To justify the risk, we have to be sure the benefit is worth it – that it actually shrunk the timeline. To just give us another data point, I find it hard to accept.