COVID reinfection has a silver lining, which could tame the pandemic

Temperatures aren’t the only ones soaring right now.

It’s the summer of reinfection, with the likelihood of contracting COVID even higher than ever, thanks to an ultra-transmissible subvariant that evades the immune system. These variants have turned what should have been a light and breezy summer to enjoy into another tough season to endure, with little room for reprieve, even outdoors.

The chart from the US Centers for Disease Control and Prevention shows an extended wave (or wall?) of infections, with cases trending slowly upwards. But sewage data — perhaps now our best indicator of COVID in communities — belies those numbers. Nearly half of national sewage testing sites reported COVID levels at 60% to 100% of their all-time high this week, CDC data shows.

There’s also Long COVID to keep in mind: early studies show that repeated COVID infections, even asymptomatic and mild ones, put individuals at increased risk of developing incipient disease, which can lead to long-term disability and even death.

We could all use a bit of good news right now, and the good news is this: COVID variants can evade antibody immunity all they want, but they’ll still have to reckon with T cells, often overlooked and not as important. fully understood the other half of the immune system.

While antibodies, specialized proteins produced by the immune system, seek out pathogens and neutralize or destroy them, they don’t last long, usually just a few months. They latch onto a specific part of a virus that can change with new variants, potentially reducing their effectiveness.

T cells, a type of white blood cell produced by bone marrow stem cells, do not prevent infection. But they are able to drastically reduce the severity of a virus, rendering a potentially deadly virus almost mute in some people.

Because their response is not limited to a specific part of the virus, as is the case with antibodies, they continue to attack, even when the virus mutates and changes shape. And their protection is much more durable, known to last for years, in some cases. Experts say the widespread buildup of T cells — from vaccine and/or infection — in the population has likely led to generally less severe outcomes for the newer variants sweeping the country.

“T cells are a kind of victory that I think is not appreciated as much as it should be,” said Dr. Duane Wesemann, professor at Harvard Medical School and principal investigator in the Division of Rheumatology. , Immunology and Allergy at Brigham and Women’s Hospital, says Fortune. It’s “not quite a silver bullet, but a composite steel bullet that worked for us and is already in our hands.”

The company is “a bit depressed because everyone is infected with new variants,” Wesemann said. “But the T cells are still hard at work, doing a good job of preventing serious disease.”

The Often Overlooked Other Half of the Immune System

New COVID subvariants like BA.4 and BA.5, currently sweeping the country, have learned to evade immunity, leading to countless reinfections, even among vaccinated people who were infected with a different subvariant just a few weeks ago.

But when we talk about immune evasion variants, we’re really only talking about antibody immunity – and that’s only half the story. There’s a whole other aspect of immunity that doesn’t get much attention, in part because T cells aren’t as well understood and are harder to study.

T cells “have played a vital role in protecting us from the worst ravages of COVID-19,” writes Ekaterina Pesheva of Harvard Medical School in a recent blog post, adding that they are the “unsung heroes” of the pandemic.

“When antibodies fail to stop the virus from entering our cells, T cells come to the rescue,” she writes. “If antibodies are the bulwark around the castle, then T cells are the elite guards inside that disable intruders, should they manage to sneak past.”

This means that T cells have played a vital role in our natural immune response to COVID and vaccines.

“Antibodies are what we rely on to prevent infection, but if someone is infected…those T-cells can dampen the course of the disease in a way that can be very dramatic,” said the Dr. Bruce Walker, director of the Ragon Institute of MGH, MIT and Harvard, a medical institute focused on disease eradication and co-leader of the Massachusetts Consortium on Pathogen Readiness – said Fortune. .

COVID infection leads to a “robust” T-cell response that lasts at least 15 months, according to a study published this spring in the journal Natural immunology. And a 2020 study published in Nature found evidence of T-cell response to another coronavirus – SARS (severe acute respiratory syndrome), an epidemic that emerged in 2002 and killed hundreds – in previously infected patients 17 years later.

Rethinking Herd Immunity

New subvariants like BA.4 and BA.5 are increasingly coming up against a wall of T-cell-based immunity in the general population, said Dr. Amesh Adalja, principal investigator at the Johns Hopkins Center for Health Security. Fortune.

Classic herd immunity – a potential endgame started by some officials at the start of the pandemic – is not possible with COVID as it continues to mutate, vaccine uptake is not where it needs to be and protection antibodies decrease. T cells, although less powerful, offer a certain level of long-lasting defence, a kind of “herd protection”.

“Everybody’s just focused on antibody-mediated immunity, but for serious diseases, T-cell immunity is very, very important, and it’s not something you can just bypass,” said said Adalja, adding that immunity is a spectrum that ranges from simply protecting against death, hospitalization and serious infections, to completely preventing infection.

Hospitalizations will undoubtedly increase during wave BA.4 and BA.5, he said. “But will they become unmanageable? It’s gotten harder and harder for COVID to do that in the United States.”

On a similar note, Walker thinks T cells “are really what’s going to turn this pandemic into something more controllable.”

“As these new variants come out and people get exposed and get infected, what we’ve seen is that generally the virulence of the disease hasn’t been as great,” he said. earlier this month. “I think a lot of it has to do with people generating some level of T-cell response.”

“For weeks, more transmissions have been occurring, but hospitalizations have not exploded. I think that speaks – at least for now – of some of the wind that has been pulled from the sails of the pandemic.

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