As the coronavirus pandemic spreads, we've asked readers what they most want to know about its impact, prevention and treatment. This is an answer to one of those questions. You can find more answers here.
If you suspect you may have already had COVID-19, is there a test that can be done after the illness has passed?
Yes, there is a blood test that looks for signs that someone had been infected by COVID-19. Also known as a serology test, it is not used to diagnose someone with the disease — that is done by taking nasal or oral samples using cotton swabs for a different type of test. Instead, the serology test looks for antibodies, which are proteins in the blood that are produced as part of the body's immune response to infection. These are usually most detectable after someone has recovered from the illness.
The hope is that antibody testing will provide new options for people and public health policymakers. If we can identify those who have COVID-19 immunity, perhaps more people can safely be deployed on the front lines, such as health care, grocery stores, transit drivers, child care and other critical jobs. It would also be valuable information for family caregivers, co-workers and for anyone trying to get back to a normal life.
For public health officials, the antibody testing can be used to help provide estimates on what share of the population could be immune from the new coronavirus. That would inform decisions about when and how to lift stay at home and other restrictions.
Health officials and doctors, however, caution that at this point the antibody tests results do not come with ironclad certainty. That's because we still don't know everything about COVID-19 immunity. And, unfortunately, some tests are not as good as others and some could even be fraudulent, marketed by those who exploit the fear caused by the pandemic.
"We have a lot to learn in terms of how long an immunity to this virus lasts," said Matthew Binnicker, director of the clinical virology lab at Mayo Clinic in Rochester.
"What we don't know yet is how long the antibodies persist and whether they provide strong immunity against the virus."