How Long Does COVID-19 Immunity Last?
A new study from King’s College London inspired a raft of headlines suggesting that immunity might vanish in months. But of course, the truth is complicated, and so is interpreting the study without a degree in immunology. So let's break down to get the real scoop!
A lot of depressing headlines were coming out. ”Immunity to COVID-19 Could Be Lost in Months,” The Guardian declared last week, drawing on a new study from the United Kingdom. Forbes grimly accelerated the King's College "months" timeline: “Study: Immunity to Coronavirus May Fade Away Within Weeks.” And the San Francisco Chronicle took things to a truly dark place: “With Coronavirus Antibodies Fading Fast, Vaccine Hopes Fade, Too.”
To sum up the study (very vaguely), researchers at King’s College London had tested more than 90 people with COVID-19 repeatedly from March to June. Several weeks after infection, their blood was swimming with antibodies, which are virus-fighting proteins. But two months later, many of these antibodies had disappeared.
What?!?! If our defenses against COVID-19 disappears in weeks, the virus has no chance of being a 'one and done' and say goodbye to herd immunity solution. Even worse, this could mean that vaccines that work on the basis of antibody response would be useless after a few months.
Some background: Acquired immunity is cellular memory. When our bodies fight off an infection, we want our immune systems to remember how to defeat it again, like a person who, after solving a big jigsaw puzzle, recognizes and remembers how to set the pieces the next time. The whole point of vaccination is to teach the immune system those same puzzle-solving lessons without exposing it to the full virus. This is where the apocalyptic interpretation of the KCL study was founded. It found that the number of certain active antibodies—called “neutralizing antibodies”—declined significantly between tests, especially in patients with mild or no symptoms. If they plunge quickly, that might mean that our immune system can't remember how to solve COVID-19 for more than a few months at a time, dooming us to start from square one with each new exposure.
Although the KCL study is important and may be concerning, the headlines may not be worth all the hype and worry. Like most biological structures and processes found in the human body, our immune system is a fascinating, mysterious place, and the KCL study looked at one bit of it. "When a new pathogen enters the body, our adaptive immune system calls up a team of B cells, which produce antibodies, and T cells. To oversimplify a bit, the B cells’ antibodies intercept and bind to invading molecules, and the killer T cells seek and destroy infected cells. Evaluating an immune response without accounting for T cells is like inventorying a national air force but leaving out the bomber jets. And, in the case of COVID-19, those bomber jets could make the biggest difference. A growing collection of evidence suggests that T cells provide the strongest and longest-lasting immunity to COVID-19—but this study didn’t measure them at all."
That being said, to try to understand your body's immune response by only studying one piece of it, is very incomplete, especially if our body's, suspect, best defense against COVID-19 is not the piece being studied. A study from France’s Strasbourg University Hospital, found that some people recovering from COVID-19 showed strong T-cell responses without detectable antibodies. Thus, if a similar study was performed looking at T-cell response to COVID, the results (and headlines to follow) might be more optimistic.
“It’s possible that previously-infected people could utilize [immunological memory] responses to produce new antibodies in case they are exposed to SARS-CoV-2 again,” Pamela Bjorkman, a biochemist at the California Institute of Technology, wrote in an email between her and The Atlantic. “So I would not conclude yet that people infected with SARS-CoV-2 are not protected from another infection.” What does that mean? Thompson does a great job unpacking this theory: "Let’s say I learn to solve a Rubik’s Cube. Three weeks later, you might ask me how I did it. I can’t really describe every step from memory, I tell you. But then you hand me a Rubik’s Cube, and I suddenly recall my strategy and solve that sucker in half the time. Similarly, the KCL study might initially seem to describe a forgetful antibody response. But, primed by the reappearance of COVID-19, our immune system might snap back and mount a powerful defense."
Beyond these three caveats to the panic-stricken headlines, several other developments offer a reason to be hopeful that the pandemic won’t last forever. Vaccine research is continuing to blast ahead at an inspiring pace. Several studies on monkeys, whose immune systems are as close to ours as that of any animal, have been promising, showing a strong and lasting immune response. And a recent paper shows that 17 years after SARS first struck East Asia, many patients have “long-lasting T cell immunity” that might even be helping them fight COVID-19, a k a SARS-2. In summary:We are still facing a dangerous disease and learning more every week. Good news is that the immune system is a big, complicated place, and no single study looking at one part of that big, complicated place should convince you that a vaccine is doomed and the pandemic will be with us forever.