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Coronavirus: What antibody testing can and can't tell Minnesota

Minnesota has not yet rolled out widespread antibody testing.

What exactly can antibody testing do for Minnesotans during the coronavirus pandemic?

When Gov. Tim Walz announced recently that the Mayo Clinic and University of Minnesota are in the process of building out the capacity to perform tens of thousands of antibody tests – also called serologic tests – per day, it provided hope that the tests could speed up the state's ability to get more of the approximately half-a-million unemployed residents back to work. 

The serologic test is a blood test that can find the presence of antibodies to the novel coronavirus (SARS-CoV-2), indicating that a person was previously infected, with the U of M saying in a release April 16 that "those who have previously contracted COVID-19 and are now assumed to be immune to it." 

But assuming immunity is a lot different than knowing for fact that immunity exists, and therein lies a current limit to the effectiveness of the tests as it pertains to getting people back to work.

"We don't know if someone who has antibodies – they're exposed to the virus that causes COVID-19 – if they will be protected from disease. People are actively doing research on this now and we just don't have information on that yet," said Minnesota State Epidemiologist Dr. Ruth Lynfield on Tuesday.

"We also don't know, if there is protection, how long it lasts. Does it last for 6 months? Does it last for a year? Does it last for 2 years? We don't know." 

In mid-April, South Korean health officials reported 163 patients who had fully recovered from COVID-19 tested positive for a second time. As NPR reported, there are a few theories for why patients tested positive again. 

  1. Remaining virus in their bodies reactivated. 
  2. Virus may be able to stay dormant before reactivating. 
  3. Tests picked up dead virus particles that aren't infectious or transmissible. 

"Another issue is whether the antibody is protective or not. There are certain kinds of serological tests that are measuring antibody, but they are not measuring what we call neutralizing antibody," Lynfield explained. 

"In order to do that, you need to have cells that have virus growing on it and you put the person's serum in different solutions and you see if the antibody that is present can prevent that virus from replicating, or neutralize the virus."

She said most serologic tests can only detect an antibody, not reveal if the antibody has the neutralizing ability. 

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So how can the tests help?

Although it's impossible at this point to guarantee immunity or say for certain that someone has neutralizing antibodies, serologic tests do serve a useful purpose. 

"A good use would be to understand on a population level how many people may have been exposed to this virus. That can help us understand the scale of the pandemic in Minnesota community," said Lynfield. 

What's more is that there is research being done now to find out if recovered COVID-19 patients' convalescent plasma can help people still fighting the disease, which is currently the subject of clinical trials at the Mayo.

Here's more on the convalescent plasma study and how it works, according to the Mayo Clinic:

"It turns out that for some other diseases caused by viruses, giving people the liquid portion of blood (plasma), obtained from those who have recovered from the virus, leads to more rapid improvement of the disease. Patients with COVID-19 may improve faster if they receive plasma from those who have recovered from COVID-19, because it may have the ability to fight the virus that causes COVID-19.

"Initial data available from studies using COVID-19 convalescent plasma for the treatment of individuals with severe or life-threatening disease indicate that a single dose of 200 mL showed benefit for some patients, leading to improvement.

"COVID-19 convalescent plasma has not yet been demonstrated to provide clinical benefit in patients affected by this disease. It's not known if this treatment will or will not help those with COVID-19 or if it will have any harmful effects, but this is one of the only treatments that we have at present."

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