HN Headline may be misleading. The article's headline is: "Many Trial Volunteers Got Placebo Vaccines. Do They Now Deserve the Real Ones?"
Well, it's always a concern. However, having a chance at getting a vaccine, even if it's 50%, and the likelihood of some protection is a whole lot better than 0% of getting any protection. Plus, we have to have these trials and the development of these vaccines before life can get back to any semblance of normal.