What Do We Know About COVID-19 Immunity and Antibody Testing?

Conversations abound about the best (and fastest) way to reopen the world’s economies in the wake of the COVID-19 pandemic. While there are many factors involved in making these difficult decisions, including preventing as many deaths as possible, you’ve probably heard a lot about antibody testing and figuring out how many people are now immune to COVID-19 and for how long.

There’s still a lot we don’t and can’t know about immunity to COVID-19, even as more than 70,000 people have now recovered in the United States. The coronavirus, which primarily causes a respiratory infection, has only been around in humans since December 2019. Determining COVID-19 immunity will require months and years to collect the most accurate data, but it’s still important to start investigating these questions now.

Here’s what we know about COVID-19 immunity and antibody testing so far:

Will You Develop COVID-19 Immunity?

When your body fights most viruses, including other coronaviruses that have circulated in humans for a long time, it develops antibodies to help neutralize the virus if it comes back again. A typical immune response will first develop immunoglobulin M (IgM) antibodies before developing longer-term immunity in the form of immunoglobulin G (IgG) antibodies as virus levels go down. It’s these IgG antibodies that experts are looking at to determine COVID-19 immunity.

According to Elizabeth McNally, M.D., Ph.D., director of the Center for Genetic Medicine at Northwestern University Feinberg School of Medicine, early research indicates so far that SARS-CoV-2, the coronavirus that causes COVID-19, generally follows a typical immune response pattern. However, once people develop antibodies, there are still questions about whether or not the antibodies are protective and could fight off a future infection and, if so, how long that protection lasts.

McNally highlights that SARS-CoV-2 is “an unusual virus” with a couple of features that look a bit different. For one, some people who get COVID-19 develop an overactive immune response referred to as a cytokine storm where those antibodies attack a person’s entire system and cause very serious complications. COVID-19 also seems to cause more lingering than other coronaviruses, like those that cause the common cold.

Regardless of these differences, however, McNally and other experts believe we can expect some level of protection against COVID-19 after exposure. Humans typically develop immune system protection against the four coronaviruses that cause the common cold for a few years before it wanes. Based on what we know so far about COVID-19 and past data from others like SARS-CoV-1 (SARS), it seems most humans will develop SARS-CoV-2 immunity for up to a year at least.

“Sometimes you have to act on a historical basis,” Anthony Fauci, M.D., director of the National Institute of Allergy and Infectious Diseases, explained during a JAMA livestream. “If we get infected now and it comes back next February or March, we think this person is going to be protected.”

What Is Antibody Testing for COVID-19?

Antibody testing — also called serological testing — is the tool doctors and researchers use to determine whether or not you’ve developed antibodies against a specific virus. Widespread antibody testing is critical to understanding the true impact of COVID-19. Because of testing shortages in the United States, people who likely had a milder case of COVID-19 stayed out of the hospital and haven’t been tested.

“Our view is somewhat biased because we’ve been looking at those people who are really sick in the hospital,” Dr. McNally told The Mighty. “There’s a whole group of people who’ve had this now who’ve recovered from it, and we don’t have a lot of data about what their immune responses look like.”

Like other types of lab testing, COVID-19 antibody tests won’t be perfect every time. It takes several weeks to develop IgG antibodies against the novel coronavirus, so testing requires some patience as people recover. And, everybody responds differently. “A lot of people are getting [COVID-19] and humans are incredibly variable and immune responses are incredibly variable,” McNally said.

In addition, a serological test can tell you the level of antibodies in your system, but researchers still need to understand what level of antibodies provide protection. McNally said it’s also important to discover what part of the virus antibodies respond to. Another challenge is making sure antibody tests can distinguish between antibodies for the coronavirus that causes COVID-19 and other types of coronaviruses people have been exposed to for years.

Antibody testing right now must be done primarily in health care settings, which McNally said isn’t ideal because people should still be staying home as much as possible to prevent the spread of the virus. Ideally, an accurate at-home test kit will help speed up testing. Overall, it’s just going to take more time until we have enough accurate information to pin down COVID-19 immunity.

Can You Be Reinfected With COVID-19? 

While it’s too early to say with 100% certainty, McNally said potential COVID-19 reinfection or reactivation as the norm is unlikely, despite viral news stories to the contrary. Though there may be some rare cases where this can happen — like in any other virus — what’s reported as COVID-19 reinfection probably has another explanation.

For example, the reverse transcription polymerase chain reaction (RT-PCR) tests used to diagnose COVID-19 rely entirely on having enough virus to measure. If a swab sample isn’t collected well or there’s not much virus in the sample, the test will come back negative. A later test may come back positive because the virus stays in a person’s system a bit longer. It’s not a reinfection.

“You have to be careful looking at those data and I certainly wouldn’t extrapolate that to the rest of the regular population,” McNally cautioned. “The stories like that are very rare, but they are the ones that get in the news. It’s a little like a shark attack. It’s the stuff you end up hearing about.”

The Takeaway

Learning more about COVID-19 immunity and the scope of infection through antibody testing is a key next step in recovering from the pandemic. The Food and Drug Administration (FDA) is working to identify accurate antibody tests. The Centers for Disease Control and Prevention (CDC) and National Institutes of Health (NIH) have both started large-scale serological studies to look at COVID-19 exposure and potential immunity in communities across the country.

And regardless of the unknowns about COVID-19 immunity we’ll have to live with for a while longer, McNally highlighted that there’s cause for some cautious optimism.

“It’s always important to say we’re making our best guess based on limited information available to us,” McNally said. “It’s really no different from how all of our testing works, but it’s a scary time. So I think it’s important to reiterate that most people who get this are going to do just fine with it.”