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 limited to increasing the chances of success for the convalescent plasma treatment for COVID-19, a multi-site project now underway via an alliance including Mayo and dozens of high-profile universities across the country.

The test is also seen as a more meaningful metric of a person's potential for immunity, should the science mature enough to answer the question of whether having previously contracted the virus grants a person immunity, and if so, for how long.

Currently, the status of serological testing for COVID-19 is that of a science that has not lived up to its potential.

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Greeted just two months ago as a resource with the potential to tell people they were free to move about without worry, it has been hobbled by a crush of tests of uncertain quality and health officials' unwillingness to assert that even a validated determination of being serology positive offers an individual useful information about their safety when re-exposed to the virus.

Minnesota has been fortunate in that the tests produced by Mayo Clinic and the University of Minnesota have been FDA-validated, and state health officials have repeatedly spoken of plans for population-based testing using those assays.

Among other uses, these studies could help determine how lethal the illness really is. But long-promised statewide studies employing serology to determine what percent of the state has contracted the virus have yet to materialize.

The new Mayo antibody test was developed in partnership with a trio of private interests, including Rochester-based Vyriad, Inc. and Imanis LIfe Sciences, as well as the New York-based biotech giant Regeneron.

Also on Thursday, health officials reported another 435 cases of COVID-19.

The cases were distributed widely across the state, with 41 counties showing new cases, most in the single digits. Mower County has continued its spike in cases, posting 30 more cases Thursday, while Dakota County numbers were disproportionately high with 52 cases.

The state reported 13 deaths from the illness Thursday, bringing the total number of lives lost to the illness in the state to 1,249. One death each was reported in Scott, Dakota, Anoka and Morrison counties, with two deaths reported in Ramsey County and seven in Hennepin County.

The state set a new one-day testing record by reporting the processing of 12,071 samples Thursday. The spike in new testing was driven by four community testing clinics created by the Minnesota Department of Health in Minneapolis and St. Paul in response to the widespread gathering for protest in recent weeks, as well as the ensuing call by health officials for all those who attended to seek testing, whether they have symptoms or not.

In a hopeful sign, the number of patients treated in ICU settings for COVID-19 in the state continues to remain relatively stable, climbing just two beds to 196. An additional 215 Minnesotans were hospitalized in non-ICU settings for COVID-19.

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Minnesota Department of Health COVID-19 hotline: 651-201-3920.

COVID-19 discrimination hotline: 833-454-0148

Minnesota Department of Health COVID-19 website: Coronavirus Disease (COVID-19) website.