For one, a serologic test can reveal whether a person might have developed immunity to COVID-19. Researchers haven’t determined yet whether a person who has had and recovered from COVID-19 is protected from getting it again. But anecdotal evidence from China; preliminary studies in animal models; and experience from previous outbreaks, like severe acute respiratory syndrome and Middle East respiratory syndrome, suggest this might be the case.
Having a serologic test may provide the opportunity to tell, for example, whether health care workers have developed immunity. Although such health care workers would still be required to wear personal protective equipment, they would be at lower risk for getting re-infected, compared to health care workers who do not have this immunity.
A serologic test also might be used to determine the levels of COVID-19-related antibodies in a person’s blood ― information that may be useful in the experimental treatment known as convalescent plasma therapy. Plasma is the component of the blood with no blood cells. The idea behind this treatment, which involves giving patients an infusion of antibody-rich plasma from those who have recently recovered, is that COVID-19 antibodies might neutralize the virus or jump-start a patient’s own immune response. Researchers studying COVID-19 in China have suggested in two small case studies of patients that this pre-antibiotic era approach to treating infectious diseases might be a useful tactic in the pandemic. But studies of previous coronaviruses suggest that donors need to have high levels of antibodies in their blood for the therapy to work.