Health officials have yet to determine if previously contracting the illness offers protection 5:02 pm, Jun. 11, 2020 × Mayo Clinic. Forum News Service file photo ROCHESTER, Minn. — Mayo Clinic on Thursday, June 11 announced it had developed a refinement of its serological test for COVID-19. It is a blood assay that detects not just whether someone has contracted COVID-19 and developed antibodies, but whether they have developed a specific, more effective form: so-call "neutralizing antibodies" capable of fighting off the illness. The test's utility at this point is largely lim...