This wasn't a double blind trial. This was a "Do something and watch the results" activity. And consider this: "In these people, we were able to identify cells

This wasn't a double blind trial. This was a "Do something and watch the results" activity. And consider this: "In these people, we were able to identify cells stimulated by a key antiviral defence response in both the nose and the blood. This response, called the “interferon” response, is one of the ways our bodies signal to our immune system to help fight off viruses and other infections. We were surprised to find that this response was detected in the blood before it was detected in the nose, suggesting that the immune response spreads from the nose very quickly." This told us that one of our hypotheses about the virus was invalid. You don't need a lot of volunteers for that.