 Human infection studies are a type of research that involve the deliberate infection of volunteers. Human infection studies allow scientists to monitor an infection from the very moment it begins and to know when that infection happens and to make especially detailed measurements of the immune response to that infection. The researcher infects a human with different pathogens. This infection is under well-controlled conditions, but it gives us enormous opportunities to understand how the pathogen interacts with the human and how you can actually work on the process of identifying, for example, a vaccine, a drug, or develop a new diagnostic tool. The argument is that if we can use human infection studies, it may be possible for us to develop vaccines faster. When we have over 200 candidates, it isn't possible for us to take those 200 candidates through clinical testing. It would be a very expensive exercise to do human testing for all of the candidates. So if we wanted to down-select vaccines, select only those that have the best chance of success, then we could potentially do that in human infection studies. We can also use a COVID-19 human challenge model to try to find that part of the immune system that may be protected. We could also use these challenge models to try to look at transmission of COVID-19, something that has been difficult to do during the current pandemic. Every time we do research, especially research that places a lot of demands on research participants, we need to be careful that the likely scientific benefits or public health benefits outweigh the risks of the research. And in the case of COVID-19 vaccines, those risks and benefits might be changing all the time as we learn about vaccines in other types of research as we learn more about risks. And so it's very important that the risk-benefit assessment to ensure that benefits outweigh risks is done very systematically for this disease and in a very up-to-date fashion before the research starts. We need to make sure that when we select participants, we select the ones who are in the safest possible age groups. Right now, it's looking like younger people are more likely to be good volunteers. In addition to that, you have to make sure that you have experienced sites and investigators so that people get the best care possible while they are in these studies. We would like to have what we call rescue therapy or a drug that we can give that can stop the progression of COVID-19 illness. We also have to identify suitable facilities where these studies could be done. We would want to make sure that if a COVID-19 human infection model were to be done, the facility could ensure that isolation rooms were available with proper airflow, that staff had proper PPE, that all of the medical support that's necessary should a patient or should a volunteer become quite ill with COVID-19, all of the necessary medical support were there to treat them. So human infection studies for COVID-19 vaccine development should be done now. I think this is the right time. The right time because I think that we need this very fast. We know that the situation worldwide is not good. We need to actually eliminate this virus as soon as possible and the best way to do it is by doing the human infection studies. There are some high level containment units around the world that have been built especially to treat patients that have highly contagious diseases like COVID-19. For a large vaccine study using a COVID-19 human challenge model, for instance, to look at efficacy of a COVID-19 vaccine, you would likely need to use several of these high level containment units to get enough volunteers to do the study.