COVID reinfection may have a silver lining one that could help minimize the pandemic’s impact

The summer of reinfection is upon us, with the likelihood of getting COVID yet again higher than ever. That’s thanks to an ultra-transmissible, immune-evading subvariant that has mutated what should have been a light, breezy summer into yet another heavy season to be endured—with few opportunities for reprieve even outdoors.

In addition to CVID, there is Long COVID: Early studies show that repeat infections of the virus even asymptomatic and mild ones put individuals at greater risk for the nascent condition, which can result in long-term disability and even death.

The good news is that COVID variants can evade antibody immunity, but they will still have to contend with T cells, which are often overlooked and not as well understood as antibodies.

Antibodies, specialized proteins produced by the immune system and designed to incapacitate or destroy pathogens, do not last long. They latch onto a specific part of a virus that’s subject to change with new variants and potentially reduce their efficacy. T cells, a type of white blood cell produced by stem cells in the bone marrow but not designed to prevent infection or Long COVID, but capable of dramatically reducing severity in some individuals depending on their body’s T-cell response.

Because they respond to more parts of the virus, T cells are less affected by mutation than antibodies. They can even continue to attack the virus even if it mutates and changes shape. And their protection is much more durable, known to last for years, in some cases. Experts say that widespread accumulation of T cells—from vaccine and/or infection—in the population has likely led to generally less severe outcomes for new variants sweeping the country.

Dr. Duane Wesemann, a professor at Harvard Medical School and a principal investigator in the Division of Rheumatology, Immunology, and Allergy at Brigham and Women’s Hospital, told Fortune that T cells are “not quite a silver bullet—but a composite steel bullet that’s worked for us and is already in hand.”

 Wesemann said that society is “depressed a little bit,” because everyone is getting infected with new variants of the virus. But T cells are still at work, preventing severe disease by killing off infected cells.

 The immune system’s other half is the human brain

 New subvariants of the COVID virus—BA.4 and BA.5—have learned to evade immunity, leading to countless reinfections—even among vaccinated people who were infected by a different subvariant just a few weeks ago. But when we talk about immune-evading variants, we’re really only talking about antibody immunity—and that’s only half of the story. There’s a whole other side of immunity that doesn’t get much attention in part because T cells aren’t understood as well and are more difficult to study

 The virus can enter a cell by crossing the membrane. If antibodies do not stop the virus from getting into our cells, T cells come to the rescue. If antibodies are the rampart around the castle, then T cells are the elite guards inside it that disable intruders, should they manage to sneak in.

 T cells have been a critical part of our natural immune response to both COVID and vaccines. Antibodies are what we rely on to prevent infection, but if somebody becomes infected … those T cells can attenuate the course of the disease in what can be a very dramatic way, according to Ragon Institute of MGH, MIT, and Harvard director Bruce Walker. 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 the concept of herd immunity

 According to Dr. Amesh Adalja, a senior scholar at the Johns Hopkins Center for Health Security, new subvariants such as BA.4 and BA.5 are increasingly running up against a wall of T-cell based immunity in the population at large—classic herd immunity is not possible with COVID because it continues to mutate, vaccine uptake isn’t where it needs to be, and antibody protection wanes. T cells, while less potent, offer some level of durable defense against severe infection at a population level—a “herd protection” of sorts, though how much T cells help an individual depends on their body’s individual response.

 “Everyone focuses only on antibody-induced immunity, but for severe disease, the T-cell immunity is very, very important—and it’s not something you can just get around,” said Joseph Adalja of the University of Pittsburgh Medical Center. “Immunity is a spectrum that ranges from merely protecting against death and hospitalization to preventing infection altogether. Hospitalizations will undoubtedly rise during the Barmoths and Black Harbingers, but will they become unmanageable? That’s become increasingly difficult for COVID to do in the U.S.”

“For weeks now, more transmission has been occurring, but hospitalizations have not increased dramatically. I think this may be an indication that the virus has lost some of its momentum.”

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