As the United States works overtime to screen thousands for the novel coronavirus, a new blood test offers the chance to find out who may already have immunity.
Such a test could be a game changer in the battle to contain infections and get the economy back on track.
Several academic laboratories and medical companies are rushing to produce blood tests which can quickly identify disease-fighting antibodies in people who already have been infected and recovered.
Many who contract the illness suffer only mild symptoms before recovering. Others may have recovered without knowing it, having shown no symptoms at all.
Researchers at New York's Mount Sinai's Icahn School of Medicine in New York say they have developed one of the first antibody tests in the United States for COVID-19, the disease caused by the new coronavirus.
One researcher tells Reuters, "people who are immune could be the first people to go back to normal life and start everything up again."
Several private companies have begun selling blood tests for COVID-19 antibodies outside the United States.
Such tests are relatively inexpensive and simple, usually using blood from a finger prick.
Some can produce results in ten to 15 minutes. That could make ramping up screening much easier than for diagnostic tests.
For now, the true number of people who have been able to fight off the virus is unknown.
Also unknown: how long immunity might last.
Some public health experts say that if immunity testing goes forward on a wider scale, healthcare workers and first responders should take priority.
The U.S. Centers for Disease Control and Prevention said it is working on its own version of antibody tests, but it has not given a timetable. The agency has said extensive research is underway.