COVID reinfection has a silver lining – one that could tame the pandemic


COVID reinfection has a silver lining - one that could tame the pandemic

Not only the temperatures are shooting up at the moment.

It’s the summer of reinfection, and the odds of catching COVID are once again higher than ever thanks to an ultra-transmissible, immune-evading subvariant. These variants have turned a light, breezy summer into another tough season to endure – with few opportunities for respite, even outdoors.

The US Centers for Disease Control and Prevention chart shows an extended wave (or wall?) of infections, with cases slowly trending upwards. But wastewater data — perhaps now our best predictor of COVID in communities — belies those numbers. Almost half of the state’s sewage testing sites were reporting COVID levels at 60% to 100% of their all-time highs as of this week, according to CDC data.

There’s also Long COVID to consider: Early studies show that repeated COVID infections — even asymptomatic and mild ones — put individuals at higher risk for the nascent condition, which can lead to long-term disability and even death.

We could all use some good news right now, and the good news is this: COVID variants can evade antibody immunity as much as they want – but they still have to deal with T cells, which are often ignored and not so… well-understood other half of the immune system.

While antibodies, specialized proteins produced by the immune system, seek out pathogens and disable or destroy them, they don’t last long — usually just a few months. They attach themselves to a specific part of a virus, which can change with new variants, potentially reducing its effectiveness.

T cells, a type of white blood cell produced by stem cells in the bone marrow, do not prevent infection. But they are able to dramatically reduce the severity of a virus and all but silence a potentially deadly virus in some individuals.

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 permanent, and in some cases has been known to last for years. Experts say the widespread accumulation of T cells – from vaccines and/or infections – in the population has likely led to generally less severe consequences for new variants flooding the country.

“T cells are a type of asset that I don’t think are valued as they should be,” Dr. Duane Wesemann, a Harvard Medical School professor and senior investigator in the Department of Rheumatology, Immunology and Allergy at Brigham and Women’s Hospital wealth. They’re “not quite a silver bullet — but a composite steel bullet that worked for us and is already in our hands.”

Society is “a bit depressed because everyone is infected with new variants,” said Wesemann. “But T cells are still at work and doing a good job of preventing serious diseases.”

The often neglected other half of the immune system

New COVID subvariants such as BA.4 and BA.5 currently sweeping the nation have learned to evade immunity, resulting in countless reinfections – even in vaccinated individuals who contracted another subvariant just a few weeks ago had.

But when we talk about immune-avoidant variants, we’re really only talking about antibody immunity – and that’s only half the story. There’s a whole other side of immunity that doesn’t get much attention, partly because T cells aren’t as well understood and are more difficult to study.

T cells “have played a critical role in protecting us from the worst of COVID-19’s ravages,” Harvard Medical School’s Ekaterina Pesheva wrote in a recent blog, adding that they are the “unsung heroes” of the pandemic .

“When antibodies don’t stop the virus from entering our cells, T cells come to the rescue,” she writes. “If antibodies are the wall around the lock, then T-cells are the elite sentinels inside, incapacitating intruders if they manage to sneak in.”

This means that T cells were a crucial part of our natural immune response to COVID and vaccines.

“Antibodies are what we rely on to prevent infection, but when someone does become infected… these T cells can slow down the progression of the disease in very dramatic ways,” said Dr. Bruce Walker, director of the Ragon Institute of MGH, MIT and Harvard, a medical institute focused on disease eradication, and co-chair of the Massachusetts Consortium on Pathogen Readiness – narrates wealth. .

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

Rethinking herd immunity

New subvariants such as BA.4 and BA.5 are increasingly encountering a wall of T cell-based immunity in the population, said Dr. Amesh Adalja, Senior Scholar at the Johns Hopkins Center for Health Security Wealth.

Classic herd immunity — a potential endgame brought up by some officials early in the pandemic — is not possible with COVID as it continues to mutate, vaccine uptake isn’t where it should be, and antibody protection is waning. T cells, while less powerful, provide a degree of ongoing defense—a sort of “herd protection.”

“Everyone just focuses on antibody-induced immunity, but in severe disease, T-cell immunity is very, very important and you can’t just bypass it,” Adalja said, adding that immunity is a spectrum that’s derived from mere ranges from protection against death, hospitalization and serious infection to complete prevention of infection.

Hospitalizations will no doubt increase during the BA.4 and BA.5 waves, he said. “But do they become unmanageable? This is becoming increasingly difficult for COVID in the US.”

Similarly, Walker believes that T cells “are really what’s going to turn this pandemic into something more controllable.”

“As these new variants emerge and people are exposed and infected, what we have seen is that the virulence of the disease has generally not been as great,” he said earlier this month. “I think it has a lot to do with humans generating some level of T-cell response.”

“There have been more transmissions for weeks, but hospital admissions have not gone through the roof. I think it says – at least for now – that some of the wind has been taken out of the sails of the pandemic.”

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