What Are Antibody Tests, and Can They Prove Coronavirus Immunity?
Researchers are working on tests that look for the body's response to Covid-19 infection, and politicians keep talking about them as a way to end lockdowns. Here's what the science says.
There was a time when waking up with a scratchy throat or a dry cough didn’t elicit such a sense of dread, but Covid-19 has made us all hyper-aware of its symptoms. Many people have been left wondering if they are asymptomatic carriers of the disease, or if a slight cold they may have recently experienced was actually something more menacing.
These fears are not unfounded: More than a million patients around the world have confirmed cases of coronavirus, but the real number of infections is far higher—though nobody yet knows by how much.
That’s why medical professionals are rushing to develop tests for antibodies that might reveal if a patient ever contracted Covid-19, regardless of whether they experienced symptoms. These tests may even be able to determine individual immunities to the virus, which has led to speculation that some people could reenter the workforce or resume normal activities if they have the right antibodies.
While this proposed solution may provide a sense of hope, it is far from a certain outcome at this point in time. There’s no clear consensus about the immunological response to Covid-19, and murky ethical problems undergird the idea of lifting restrictions on some populations, while isolating others, especially based on unsettled science.
What are Covid-19 antibody tests?
Antibody tests, also known as serological tests, differ from the diagnostic swab tests that have been in high demand since the pandemic gained momentum.
Swab tests, or PCR tests, are designed to directly detect the virus by searching for its RNA, which is a genetic signature of its presence. These tests require collection of mucus samples from patients, typically sourced from deep within the nasal cavity, which are then sent to a laboratory to be examined. If the results come back positive, the patient is considered an active carrier of Covid-19 who could potentially infect other people.
Antibody tests, in contrast, don’t look for the virus itself, but rather our immunological response to it. When our bodies are invaded by antigens such as the coronavirus, our immune systems react by creating a type of blood protein called an antibody. Antibodies flow through the blood, attacking the alien antigens by binding to them, which can neutralize the spread of infection. Many known antibodies can be detected with a quick blood test.
“The idea is that you have volunteers who have recovered from infection, and you look to see what antibodies they’re expressing and test that against samples of the virus, basically, to see what are the circulating antibodies that recognize your virus,” said Ruth Collins, professor of molecular medicine at Cornell University College of Veterinary Medicine, in a call.
It can take several weeks for the immune system to develop antibodies to fight a virus, which means positive serological tests may not indicate an active infection. Instead, the presence of coronavirus antibodies demonstrates if a patient ever had Covid-19, whether or not they experienced symptoms.
While it is common for an exposed person to develop immunity to other known viruses, it is important to emphasize that nobody knows yet whether the presence of Covid-19 antibodies indicates that a patient has either temporary or permanent immunity to the infection.
“We don’t know yet exactly how people’s immune systems respond to the infection, so we’d have to find something that would mark everybody’s response to the virus—the universal human response to the virus—and to make sure that it was specific to this virus,” Collins said.
“These things are doable,” she added, “they just take a long time to work out.”
How effective are antibody tests for the coronavirus?
Short answer: We have no idea.
Countless teams of scientists around the world are developing serological tests to detect antibodies related to Covid-19, including researchers at the Centers for Disease Control (CDC). Last Thursday, the US Food and Drug Administration approved the first test for antibodies test for Covid-19, though it is intended as a diagnostic test for active infections.
Last week, a team of scientists at Stanford University conducted finger-prick blood tests on 3,200 volunteers to help refine their antibody test. Likewise, in Italy, an entire town of 3,000 people that already received swab tests is now in the process of providing blood samples to follow-up on the diagnostic data with antibody studies.
Regardless, there have also been setbacks with the roughly 100 test kits for these antibodies that are already in development. None of these tests are close to reaching the high bar required for public distribution.
"There’s so much we really don’t know"
“You’d have to have a very high specificity and sensitivity, so you would be able to pick up even small amounts of those antibodies or the evidence of infection in people's blood,” Collins said. “Without that, you could well have people that have been infected without knowing about it,” she continued, or “people who might think they were still naive, immunologically, when in fact they weren’t.”
In other words, antibody tests not only need to be good enough to yield reliable positive results, they also need to clearly show who does not have Covid-19 antibodies. Finding the right balance requires making sure that antibodies linked to viruses that aren’t Covid-19 do not produce false positives, and ensuring that the antibodies that are specifically linked to this particular coronavirus cannot evade detection.
It’s hard to predict how long this process will take, given that so many teams are actively working on it, but it’s probably optimistic to expect they will take weeks or even months to be widely available to the public.
This timeline might be further delayed by new revelations about Covid-19. For instance, it’s possible that some carriers may never develop symptoms, but could still remain infectious to others for months.
“There’s not even a consensus that everybody will completely clear the virus from their system,” Collins noted. “Some people may be asymptomatic shedders for a while. There’s so much we really don’t know.”
Could antibody tests eventually enable some people to go back to work?
The phrase “immunity passport” has been floated by the government of the United Kingdom, and others, as a potential way to allow people with immunity to Covid-19 to return to regular work and travel routines.
Assuming that widespread serological testing is achievable, the idea is that people with antibodies linked to Covid-19 would be cleared of social distancing measures because they are theoretically immune to the virus and cannot actively spread it. This would bring back some normalcy for some of the population, and it would also enable scientists to better estimate the total number of Covid-19 cases, as opposed to confirmed cases involving patients who were sick enough to receive a swab test.
On the flip side, antibody tests for this purpose raise concerns about privacy rights and employment inequities, given that authorities would be using medical information to judge whether patients can return to work and normal life. In the United States, the Americans with Disabilities Act (ADA) and the Genetic Information Act (GINA) prevent employers from discriminating on the basis of disability or genetic information. But discrimination for health reasons “remains legal in many contexts in the United States,” according to Jessica Roberts, director of the Health Law and Policy Institute at the University of Houston Law Center. "We can go some way towards knowing who has been infected, but the idea of it being used as employment criteria is somewhat dystopian” “Both laws would likely permit employers to screen employees for antibodies,” Roberts said in an email. She noted that GINA only applies to genetic test results and family medical history, which are not likely to apply to antibody tests, which do not look for individual genetic information. “Moreover, the ADA actually allows employers to discriminate if employing a person with a disability could threaten the safety of the workplace,” Roberts added. “Assuming that ADA protection applies to people with Covid-19 (which a court would have to ask whether having Covid-19 constitutes a legally recognized disability), the employer could still prohibit an employee from coming to work if the employer could show that the employee would pose a significant risk.” The notion of planning a staggered reopening of society, in which restrictions are lifted on people judged immune to Covid-19, is inherently risky on both an epidemiological and ethical level. While it may be soothing to daydream about receiving an immunity passport that allows you to return to your "normal" life, it is probably better to invest your energy in adapting to the restrictions, following health guidelines until more information is available, and working towards a better "normal" in whatever way you can. “It sounds good because it gives us what we want, which is definitive answers,” Collins said. “But we don’t know enough to be able to provide those definitive answers. We can go some way towards knowing who has been infected, but the idea of it being used as employment criteria is somewhat dystopian.”