Immunity to the coronavirus involves more than just antibodies: T cells and B cells protect us too.
According to Anthony Fauci, this suggests that vaccines should work well against variants.
More than 61 million Americans have been fully vaccinated against the coronavirus. Though some questions linger about whether the vaccines protect us against new, more contagious variants, Anthony Fauci thinks the concerns are overblown.
"I don't believe that there's anything to panic about at this point," Fauci told Insider.
That's because of a new study on T cells - a type of white blood cell that plays a key role in our immune systems - led by researchers at the National Institute of Allergy and Infectious Diseases, which Fauci directs.
The results showed that people who'd recovered from the original, or "wild type," version of the coronavirus had T cells that could recognize the variants first found in South Africa, Brazil, and the UK.
"Why it's so important to get vaccinated? Because vaccination is not only going to protect us against the wild type, but it has the potential - to a greater or lesser degree - to also protect against a range of variants," Fauci said in a White House briefing last week.
T cells aren't fazed by variants
Some of the concerns that vaccines could be less effective against variants come from lab studies involving blood samples from vaccinated people. In one such study, researchers exposed these blood samples to the variant first found in South Africa, then measured the antibody responses to that variant and to the original virus. They found that vaccinated people produced fewer antibodies that could neutralize the variant than the original virus.
Since that variant has similar mutations to the one first found in Brazil, it seemed likely that vaccines would be less effective against that strain too.
However, that research didn't look at T cells. While antibodies stop infection, your body's T-cell response can influence how severe that infection will be. A February study found that people who developed coronavirus-specific T cells within the first 15 days of their infection had milder COVID-19 than people whose T cells kicked in later.
There are two crucial types of T cells: Killer T cells identify and destroy infected cells, and helper T cells inform B cells about how to craft new antibodies.
So researchers at the National Institute of Allergy and Infectious Diseases looked at blood samples from 30 people who'd recovered from the coronavirus before the emergence of the variants. They found that their T cells did indeed respond to these variants well enough to give protection.
A similar study from the La Jolla Institute for Immunology in California reached the same conclusion. That team measured how T cells from people who'd been previously infected with COVID-19 responded to new variants. The research, which has not yet been peer-reviewed, found that after people recovered from the original virus, their T cells could respond to the variants first identified in the UK, South Africa, Brazil, and Southern California.
The same should then be true of T cells developed as a result of vaccines, since the shots prompt our immune systems to respond in the same way they would to an infection.
The La Jolla researchers have evidence that's indeed the case. They also looked at blood samples from people who'd gotten Pfizer's or Moderna's shots and found that their T cells responded just as well to the variants first found in the UK, Brazil, and Southern California as they did to the original virus.
In the case of the variant found in South Africa, T cell responses decreased by up to 33% but were still detectable. That indicates that vaccines most likely prevent deaths and hospitalizations for cases involving variants, even if they're not quite as effective against those strains.
"Would it be better if all vaccines were 100% effective in preventing infections? Of course," Alessandro Sette, an infectious-disease expert at the La Jolla Institute, told Insider. "Is it good not to die and have vaccines be 100% effective at preventing hospitalization? Yes."
T cells last months, if not years
The likeliest explanation for why the same set of T cells can recognize different variants, according to Fauci, is a phenomenon called cross-reactivity: Helper and killer T cells developed in response to a given virus are capable of reacting to a similar but previously unknown variant.
Sette compares this phenomenon to people's facial-recognition skills.
"Maybe I learn to recognize your face, then I meet your sister," he said. "It kind of looks like you, so I say, OK, that's probably someone related."
T cells are also important because they stick around for a long time.
Sette's group found in a January study that T cells in a majority of people who'd recovered from COVID-19 persisted for at least six to eight months after infection. Other research has found that white blood cells developed in response to certain viruses can last for years. T cells specific to smallpox, for example, take about 10 years to disappear after an infection.
T cells specific to SARS, a coronavirus that shares 80% of its genetic code with this new one, also linger for years. One study found responsive T cells in blood samples from people who'd survived SARS 17 years later.
Sette said he's optimistic that vaccine-induced T cells will last just as long as T cells from a coronavirus infection.
"There's no indication the immune response will rapidly decay," he said.
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