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Researchers are hoping antibody tests will help them understand who is immune to COVID-19. Getty Images
  • After an infection is cleared, antibodies continue to exist in the blood.
  • If a person were to be exposed to the same virus again, those antibodies would rush to the site of viral exposure and use their memory to blunt the virus from causing harm.
  • But if a person shows antibodies against the new coronavirus, it doesn’t necessarily mean they’re immune to reinfection.

A readily available, effective vaccine is what’s going to pull us out of the pandemic, but researchers say it’ll be several months until we reach that point.

Until then, knowing who has and has had the respiratory infection is thought to be the key to reopening the economy.

To do that, we need an open supply of two critical tests: diagnostic tests, which tell us if a person is sick with an active infection (in this case, COVID-19), and antibody tests, which tell us if a person has contracted the virus.

Using those insights, local health officials can conduct contact tracing to identify who may be at risk for contracting the virus and order specific groups or communities to quarantine, while other regions facing lower levels of infection open back up.

And health officials and medical companies have been eager to expand antibody testing.

Quest Diagnostics announced in April it will be selling at-home antibody tests that people can do themselves. The company hopes the kits, which cost $119, will tell people whether they’ve had an infection, and if they may have developed antibodies against the new coronavirus.

Big pharmacy retailers, including CVS and Walgreens, also recently announced plans to expand diagnostic and antibody testing at several store locations in hopes of identifying who has been exposed to, and potentially gained immunity against, the virus.

Even with these new tests, there are still a few issues and hurdles that stand in the way of understanding who is immune to COVID-19, according to health experts.

It’s unclear how long people with SARS-CoV-2, the virus that causes COVID-19, continue to shed the virus, and if someone has antibodies against the virus, they aren’t guaranteed to be immune.

There are also inconsistencies between all the different tests out there, and there’s an urgent need for the kits to be validated and vetted.

When a person is exposed to a virus, their immune system mounts a response that involves several types of cells and tissues that work to clear out an infection.

Antibodies are part of that mix. They’re pieces of protein that bind to a specific part of a virus, called an antigen. This action typically neutralizes, or deactivates, a virus.

After an infection is cleared, antibodies continue to exist in the blood. If a person were to be exposed to the same virus again, those antibodies would rush to the site of viral exposure and use their memory to blunt the virus from causing harm.

An antibody test involves taking a person’s blood sample and seeing if they have antibodies that attach and bind to a sample of virus. If antibodies bind to the new coronavirus, for example, this shows a person had a previous infection.

With a diagnostic test, a physician swabs a patient’s nose or throat and looks for viral genetic material to determine whether a person actively has a particular disease, like COVID-19.

The diagnostic and antibody tests don’t give us the full picture.

The diagnostic tests tell us someone has COVID-19, but they don’t tell us if and how long that person sheds the virus and is infectious others.

The antibody tests, too, pose some problems.

Simply because a person shows antibodies against the new coronavirus doesn’t necessarily mean they’re immune. Not all antibodies block viral infection.

“Antibodies are only a part of the immune response to a virus. There are other viruses where antibody responses are clearly not associated with protection,” said Dr. Otto Yang, a virologist at the David Geffen School of Medicine at UCLA.

A different test is needed to determine whether the antibodies against the new coronavirus are neutralizing, or able to bind to a virus and deactivate it.

Neutralizing antibodies doesn’t always provide protection.

“They often, but not always, correlate with immunity, as sometimes they work in concert with cellular immunity to provide immune protection,” said Dr. David Mushatt, an infectious disease specialist and section chief of infectious diseases at Tulane University.

It can also take the body up to 2 weeks to produce antibodies after an infection. A test that’s conducted too soon may produce faulty results.

Another major issue is that not all the available tests are the same, and it’s unclear how accurate they are.

That’s because in early February the Food and Drug Administration (FDA) authorized the emergency use of tests that can detect and diagnose the new coronavirus and COVID-19, meaning the organization isn’t evaluating and approving the tests before they go to market.

Because the tests haven’t been vetted or validated by the FDA, it’s unclear whether they’re all measuring the same thing.

“We don’t know if they’re all measuring the same thing, and this is one of our big challenges ahead of us,” Thomas Denny, the chief operating officer of the Duke Human Vaccine Institute, said in a recent webinar hosted by Duke University experts.

New guidance released from the Centers for Disease Control and Prevention (CDC) in late May suggests antibody tests, also known as serological tests, may be wrong up to half the time.

Antibody tests are prone to false positives because they can detect antibodies not just against SARS-CoV-2 but against other coronaviruses, such as the ones that cause the common cold, as well.

Some people who contract SARS-CoV-2 may never develop detectable antibodies after the infection clears, or their antibody levels may diminish over time and be hard to pick up on a test kit.

It can also take a while for certain people to develop antibodies after contracting SARS-CoV-2 — if an antibody test is conducted too soon, it could produce a false-negative result.

Health officials are still unsure whether the presence of antibodies means a person is protected from reinfection, and if they are, for how long.

Due to these uncertainties, the CDC advises that antibody tests should not be used to inform safety procedures involving schools, dormitories, or correctional facilities, nor should they be used to decide who is able to return to work.

“Serologic test results do not indicate with certainty the presence or absence of current or previous infection with SARS-CoV-2,” the CDC states.

This is the million-dollar question, and one that health officials are hesitant to answer. That’s because there’s no clear number of tests we need.

Health experts would like to see testing ramp up but agree we first need to validate the tests available and ensure the results are accurate.

We also need to get clearer answers regarding what the test results mean.

“We need to be patient to ensure that the antibody tests we adopt are the most accurate and predictive of immunity. It is better to wait longer for proper study and validation of these new tests than jump in too quickly and regret our decisions,” Mushatt said.

According to Mushatt, we need to determine whether the antibodies against SARS-CoV-2 confer immunity.

“Then, we can provide reassurance to those who are immune, and emphasize personal protection measures to those who are not immune,” Mushatt added.

What will likely happen, eventually, is that testing will vary from location — from state to state and even from county to county. This will largely boil down to the level of COVID-19 activity in a given area.

Dr. Michael Gunn, a professor in immunology at Duke University School of Medicine, likened the testing rollout to a forest fire.

“Once you get the fire under control, it’s an issue of managing the hot spots,” Gunn said in the Duke webinar.

We don’t need to be testing every single person in the United States on a weekly basis, Gunn noted, but rather the people who are most at risk for getting sick or have been in close contact with someone who’s been diagnosed with COVID-19.

Antibody testing alone won’t open the economy back up.

Diagnostic tests are just as much a piece of the puzzle, as they let us know who has COVID-19 in real time (and therefore should be staying at home as much as possible).

So is contact tracing, or tracking down all the people a person with an infection may have come into contact with, and quarantining those who have an infection.

“What we have to look at this as is, we have a toolbox and need a number of tools in that toolbox, and we need to use them as a team to address this,” Denny said.

On May 8, the FDA announced the authorization of the first at-home saliva-based COVID-19 diagnostic test.

The test, which was designed by Rutgers Clinical Genomics Laboratory, allows people to spit in a tube and mail it back to the Rutgers lab for testing.

This is the first at-home test approved involving saliva collection. All other approved at-home tests are conducted via a nasal swab.

The Rutgers test will hopefully expand access to people unable to easily make it to a clinic or drive-thru testing facility. The test is currently only available by prescription.

At-home diagnostic tests received scrutiny early on in the pandemic. A number of diagnostic startups, like Everlywell and Nurx, prematurely announced they’d be selling at-home diagnostic tests.

The FDA was quick to crack down on the distribution of at-home tests in late March, claiming the kits could potentially cause serious public health risks.

The FDA has since revisited the sale and distribution of at-home tests after initial evidence testing the viability of self-collected samples showed the kits could withstand being in the mail for a few days.

The FDA posted new guidelines this month designed to expedite the development and approval of more at-home self-collection kits to further expand access to testing.

Under the new guidelines, test developers are encouraged to reach out to the FDA to ensure their kits and shipping methods are in compliance with the most up-to-date regulations.