How Long Does COVID-19 Immunity Last?

[Celerity]

A new study from King’s College London inspired a raft of headlines suggesting that immunity might vanish in months. The truth is a lot more complicated—and, thankfully, less dire.

https://www.theatlantic.com/ideas/archive/2020/07/could-covid-19-immunity-really-disappear-months/614377/



They were the most depressing headlines I’d read all year. And that’s saying a lot. ”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 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.” Terrified, I read the study that launched a thousand headlines—and did not come away much less terrified. 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.

The implications seemed dire. If our defenses against COVID-19 evaporate in weeks, people could contract the disease for a second time, as some widely-shared stories have suggested. In such a world, herd immunity would be out of the question. Even more depressing, it could mean that vaccines that work on the basis of antibody response would be useless after a few months. The study conjured for me a future in which the pandemic never went away. Their response: Please calm down—but don’t expect us to make you feel entirely relaxed. (I also reached out to several co-authors of the King’s College London paper, but did not hear back.) “I was definitely very worried when I saw the headlines,” said Shane Crotty, a virologist at the La Jolla Institute for Immunology. “But then I looked at the data. And actually, looking at the data, I feel okay about it.”

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 why the KCL study initially seemed so dreadful. It found that the number of certain active antibodies—called “neutralizing antibodies”—declined significantly between tests, especially in patients with mild or no symptoms. Antibody levels are one proxy for the immune system’s memory. 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. No COVID-19 researchers are rooting for antibody levels to decline so quickly. Everyone I spoke with acknowledged that the study might reveal something important and concerning. But overall, the scientists converged on three reasons to hold out a bit of skepticism about the most apocalyptic headlines.

First, our immune system is a mysterious place, and the KCL study looked at only one part 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. “To look at just one part of the immune response is woefully incomplete, especially if many COVID patients rely more on T cells,” said Eric Topol, a cardiologist and the founder and director of the Scripps Research facility. He pointed me to a study from France’s Strasbourg University Hospital, which found that some people recovering from COVID-19 showed strong T-cell responses without detectable antibodies. “There is a chance that if a similar longitudinal study looked at T-cell response, the outcome would be far more optimistic,” he said.

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related

Immunity to COVID-19 is probably higher than tests have shown

https://news.ki.se/immunity-to-covid-19-is-probably-higher-than-tests-have-shown



New research from Karolinska Institutet and Karolinska University Hospital shows that many people with mild or asymptomatic COVID-19 demonstrate so-called T-cell-mediated immunity to the new coronavirus, even if they have not tested positively for antibodies. According to the researchers, this means that public immunity is probably higher than antibody tests suggest. The article is freely available on the bioRxiv server and has been submitted for publication in a scientific journal. “T cells are a type of white blood cells that are specialised in recognising virus-infected cells, and are an essential part of the immune system,” says Marcus Buggert, assistant professor at the Center for Infectious Medicine, Karolinska Institutet, and one of the paper’s main authors. “Advanced analyses have now enabled us to map in detail the T-cell response during and after a COVID-19 infection. Our results indicate that roughly twice as many people have developed T-cell immunity compared with those who we can detect antibodies in.”

In the present study, the researchers performed immunological analyses of samples from over 200 people, many of whom had mild or no symptoms of COVID-19. The study included inpatients at Karolinska University Hospital and other patients and their exposed asymptomatic family members who returned to Stockholm after holidaying in the Alps in March. Healthy blood donors who gave blood during 2020 and 2019 (control group) were also included.

T-cell immunity in asymptomatic individuals

Consultant Soo Aleman and her colleagues at Karolinska University Hospital’s infection clinic have monitored and tested patients and their families since the disease period. “One interesting observation was that it wasn’t just individuals with verified COVID-19 who showed T-cell immunity but also many of their exposed asymptomatic family members,” says Soo Aleman. “Moreover, roughly 30 per cent of the blood donors who’d given blood in May 2020 had COVID-19-specific T cells, a figure that’s much higher than previous antibody tests have shown.” The T-cell response was consistent with measurements taken after vaccination with approved vaccines for other viruses. Patients with severe COVID-19 often developed a strong T-cell response and an antibody response; in those with milder symptoms it was not always possible to detect an antibody response, but despite this many still showed a marked T-cell response.

Very good news from a public health perspective

“Our results indicate that public immunity to COVID-19 is probably significantly higher than antibody tests have suggested,” says Professor Hans-Gustaf Ljunggren at the Center for Infectious Medicine, Karolinska Institutet, and co-senior author. “If this is the case, it is of course very good news from a public health perspective.” T-cell analyses are more complicated to perform than antibody tests and at present are therefore only done in specialised laboratories, such as that at the Center for Infectious Medicine at Karolinska Institutet. “Larger and more longitudinal studies must now be done on both T cells and antibodies to understand how long-lasting the immunity is and how these different components of COVID-19 immunity are related,” says Marcus Buggert.

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[rzemanfl]

1. K&R. n/t

[Pobeka]

2. Thanks for posting this. I will read it with great interest. n/t

[PoindexterOglethorpe]

3. If the immunity wore off as quickly as claimed,

by now we'd be seeing a noticeable number of people getting it a second time. That does not seem to be the case.