What are antibody tests and what do they mean for the coronavirus pandemic?

As the world watches and wonders when coronavirus pandemic stay-at-home orders and social distancing measures might end, some hope antibody tests might help provide a solution.

Antibody tests — also known as serology tests — aren’t meant to diagnose active coronavirus infections. Rather, they check for proteins in the immune system, known as antibodies, through a blood sample. Their presence means a person was exposed to the virus and developed antibodies against it, which may mean that person has at least some immunity — although experts are not sure how strong the immunity may be or even how long it will last.

In contrast, diagnostic testing, so far, has mostly used a laboratory technique known as a polymerase chain reaction test or a PCR test. These tests can diagnose active infections through a sample — usually from a nose swab — that is then tested for viral genetic material.

Here are five questions and answers about Covid-19 and antibody testing.

Are novel coronavirus antibody tests available?

“Within a period of a week or so, we’re going to have a rather large number of [antibody] tests that are available,” Dr. Anthony Fauci, the director of the National Institute of Allergy & Infectious Diseases, told CNN on Friday.

But that doesn’t mean they’re ready now.

The US Food and Drug Administration has not approved any antibody tests for the coronavirus, but one test — made by Cellex Inc. — has been granted emergency use authorization. Other companies have also created their own versions under a new FDA policy implemented last month that makes it easier for companies to manufacture and distribute antibody tests.

However, the FDA tightened up the new policy and now says it will review data on lab tests that claim they can detect Covid-19 antibodies, according to Scott Becker, the CEO of the Association of Public Health Laboratories, who told CNN he was on a call with FDA officials Tuesday morning when the matter was discussed.

Since the FDA issued the policy, more than 90 developers have come forward with antibody tests, the agency said.

Under the new policy, tests can be used and distributed once the manufacturer has informed the FDA that the test has been validated, but the companies cannot make the claim that the agency has validated the tests.

The FDA has cautioned that these serology tests “should not be used as the sole basis to diagnose or exclude [coronavirus] infection or to inform infection status” and has asked manufacturers to report possible concerns over the test.

Are antibody tests accurate?

Without FDA approval, these tests don’t undergo the rigorous process usually required to prove accuracy, and this has raised concerns.

Becker has called many of the tests “crappy.” His association represents 125 state, county and municipal public health labs in the United States. Those labs, along with private labs, would be responsible for running the tests.

But Becker initially said his labs wouldn’t use the tests that are on the market because he’s concerned about inaccurate results that might mean people mistakenly believe they’re immune to coronavirus and can return to work or stop social distancing.

“It could be quite dangerous,” Becker said.

Becker said he shared his concerns about the quality of antibody tests with the US Department of Health and Human Services’ Dr. Brett Giroir and FDA Commissioner Dr. Stephen Hahn.

Becker confirmed to CNN that Hahn told him and members of his association that the National Cancer Institute (NCI) would begin reviewing data from the tests that are on the market to see if they return correct results. B

Giroir said checking these tests for accuracy will be a priority, but acknowledged not all of the available tests will be of sound quality.

“There is a very consolidated effort between the FDA, CDC, NIH to validate some of the [antibody] tests that are on the market right now … And we have reason to believe that not all of them are going to perform well,” he said at a White House press briefing last week. “We’re going to be very careful to make sure that when we tell you you’re likely immune from the disease … that test really said that.”

Wouldn’t you know if you had been exposed to the coronavirus?

Besides indicating some level of immunity, the presence of Covid-19 antibodies could help identify those who have been infected but never realized they had the disease. Early research shows a large number of people may have had mild symptoms or no symptoms at all — and this group might be spreading the coronavirus more than previously thought.

“There may be many people out there, and I suspect there are a fair amount, that have been infected, were asymptomatic and didn’t know it,” Fauci recently said on NBC News’ Today Show in response to why antibody tests are important.

The National Institutes of Health announced Friday it is recruiting up to 10,000 volunteers to take part in a study on how many Americans have been infected with Covid-19 and are not aware of it.

“These crucial data will help us measure the impact of our public health efforts now and guide our COVID-19 response moving forward,” Fauci said in a statement.

Knowing exactly who has antibodies can also help with Covid-19 treatment. Clinical trials using convalescent plasma — a process that takes the antibodies from someone who has recovered from Covid-19 and injects them into a person who is sick — are currently underway.

“How can you possibly know who to get [antibodies] from if they haven’t been tested? If you’re talking about trying to scale [convalescent plasma] up as a real therapy, you’re going to have to do mass testing to figure out who might be a donor,” Dr. Celine Gounder, a professor of medicine and infectious diseases at NYU School of Medicine, told CNN.

How long will immunity against the coronavirus last?

Those with Covid-19 antibodies might have immunity against the disease — but it’s unclear how strong the immune response might be or for how long.

“If we look at MERS coronavirus, we would see people who would have an antibody response for maybe 10 months, maybe a year,” Dr. Maria van Kerkhove, the World Health Organization technical lead for the Covid-19 response, told CNN. “Even there, we didn’t know if that conferred protection. So for this particular virus [Covid-19], the answer is we don’t know yet, but those studies are being done.”

“The immunity afforded by Covid-19 can be thought of as providing bridging protection until we have an effective vaccine available,” said Dr. William Schaffner, an infectious disease specialist at Vanderbilt, in an email to CNN.

“Even then, the vaccine may have to be given annually,” Schaffner said, pointing out that without concrete data, it’s all just speculation.

The answer may also depend on the characteristics of the virus, which we still don’t know, said Dr. Bala Hota, a professor of infectious diseases and the associate medical officer for Rush University Medical Center in Chicago.

“Some of the factors are how much variation we can expect to see in the genetic profile of infecting strains of the novel coronavirus … Since the virus is so new, we don’t have the data yet,” he said in an email to CNN.

How could antibody tests help end social distancing?

Determining who has some level of immunity through antibody testing could help people feel safer about returning to work.

New York Gov. Andrew Cuomo, whose state has more reported coronavirus cases than any other, is looking to antibody tests for “restarting life” in a city that has been brought to a halt by the virus.

New York has developed its own antibody testing regimen — approved by its department of health for use within the state — and is working with the FDA to bring it to scale, he said last week on social media.

“We cannot restart life as we knew it without testing,” Cuomo tweeted.

Former FDA Commissioner Dr. Scott Gottlieb helped devise an action plan on how to reopen the country — and antibody testing plays a crucial role.

The initiative suggests the tests will have “important implications” for people’s ability to return to work, especially in health care settings — but it also points out the many unknowns about these tests, including some pretty big ones: What does a positive test actually mean in terms of someone’s protection level? And just how accurate are they?

As those issues are addressed and testing capacity expands, the “performance of these tests improve” making it easier for the federal and state governments to establish criteria for testing and to prioritize who gets them, according to the plan. Antibody testing could also provide important data for modeling and predicting future Covid-19 outcomes.

Fauci said at a briefing that antibody tests can reveal how widespread the coronavirus is in the US: “And by the time we have to face what’s going to happen with this going back to normality, we will have in place the capability of identifying, isolating, contact tracing so that it never gets out of hand.”