Health experts are working on a COVID-19 blood test that would determine if a person who had the coronavirus is now immune. Dr. Matthew Sims, who is leading a blood sample study of over 40,000 health care workers, said the test's accuracy rate is believed to be "in the high 90s." But, there are still questions about its true success rate and how long immunity would last. Dr. Tara Narula speaks to Sims about why widespread testing is important.
