Scientists and health experts say one of the keys to reviving the economy is knowing who could still become infected by COVID-19, and who has had it and recovered — even without knowing it.”If we can identify these people, we can start to understand why their immune systems are different,” said Dr. Kaitlyn Sadtler, one of the researchers on a new coronavirus study at the National Institutes of Health.She hopes to find out how many adults in the United States have COVID-19 antibodies — especially people with no confirmed history of getting infected with it. The stakes for public health are massive.”People just want to help,” said Sadtler. “That’s why we’ve gotten so many calls for donors. People just want to do whatever they can to help.”The NIH is looking for up to 10,000 volunteers. At the same time, other efforts search for a vaccine. For now, there is no FDA approved vaccine for COVID-19, according to Dr. Arvind Venkat of the Allegheny Health Network.”There are a number of clinical trials that are going on to look at medications that have been mentioned in the press,” said Venkat, “such as hydroxychloroquine and azithromycin. And there are a number of vaccine trials, but unfortunately there are