James Hamblin: That’s a pretty high-consequence decision, especially because we might be using these passports to say who should do essential work that could put them at high risk if they aren’t actually immune.
Zhang: Exactly. If we’re using these tests to decide whether to send people out to do their jobs, that’s a big decision to make based on tests that are really new.
Hamblin: My friend went to urgent care in Culver City in L.A. and got an antibody test for IgM and IgG antibodies. These different forms of antibodies appear at different time periods after you’re infected, and you can use them to understand how recently you were infected. If you just have IgM, doctors are telling patients that it means you’ve had recent exposure to the virus and are in the early stages of infection. If you have both positive, they’re saying you have a less-recent exposure and are in the middle of an infection. If you have only IgG positive, you had a past infection and have built some level of immunity. My friend has been told he has that.
Wells: So he has some level of immunity?
Hamblin: I would think yes, though there are false positives.
Zhang: Even a validated test will have some percentage of false positives, because all tests do. We’re at this point where you get an antibody test result and think you get certainty, but in reality you just get a little bit less certainty.
Wells: Are the problems with antibody tests solvable?
Zhang: As one scientist told me, antibody tests themselves aren’t rocket science. We have antibody tests for lots of other viruses. You can go to your doctor’s office now and get a measles antibody test, for example. I could see a world in which this becomes a routine thing that you get at your doctor’s office. But right now, it’s so early that it’s hard to tell what tests actually work.
Wells: When will we have a widespread antibody test, and an understanding of what those test results say about immunity?
Zhang: Getting a test that we know works is going to come a lot more quickly than getting a test that everyone can have. With the tests that detect COVID-19, we knew how to make those months ago. We’re still not at the point where everyone can get one. The hard part isn’t going to be making the antibody test itself; it’s going to be making sure everybody can access one.
Hamblin: A few weeks ago, we were talking about antibody testing as a theoretical possibility. Now they’re here. They’re not going to be immediately perfect, but if this disease does prove to work like lots of other viruses, we should be able to have a somewhat reliable test pretty widely available within months.
Wells: Say we have a widespread, accessible antibody test. How do we use that to get people participating in society again? Logistically, what does that look like?
Zhang: No one has quite figured that out. One of the unintended but almost obvious consequences is that if you make it so that only immune people can get a job, you incentivize people to get sick so they can work, especially since so many people have lost their jobs. If that’s the case, you could have people fake their immunity certificates.