Patients in clinical trials are usually faceless. But as the experimental Covid-19 vaccine being developed by Moderna Therapeutics has begun advancing through studies, it has found a much more visible advocate: trial volunteer Ian Haydon, a 29-year-old in Seattle. Haydon has spoken about the vaccine on CNN and CNBC. He even said he’d volunteer to be exposed to the novel coronavirus, SARS-CoV-2, if researchers want to test to see if the vaccine was actually effective. But up until now he has left out a key detail: He is, apparently, one of three people in the trial who had a systemic...