Health experts are debating what to tell study volunteers who got a dummy shot instead of a COVID-19 vaccine. Should they be offered the real thing now? Others warn that giving them that option could hurt the long-term results of the studies. About half of study participants got two doses of an experimental vaccine. The others got dummy shots of salt water for comparison. The studies for the Pfizer and Moderna vaccines were intended to last two years. But with the ongoing epidemic, the companies are considering options for those who didn’t get the vaccine in the studies.