COVID-19 isn’t going away anytime soon. But for most people who do get the virus, it's packing less of a punch, thanks to immunity built up from a combination of vaccines and previous infections. In a new paper, researchers in South Korea describe in more detail how that hybrid immunity works.

It turns out that, when it comes to SARS-COV-2 viruses in the Omicron family, the part of our immune system that relies on T cells—which store long-term memory of every virus, bacteria, or pathogen we encounter—improves with every vaccine and infection. Using human immune cells in the lab, the scientists tested T cells from vaccinated people who had been infected with different Omicron viruses against variants that had emerged after their infections, and found that the T cells targeted those, too. That’s because these cells focus on conserved parts of SARS-CoV-2 that remain similar among the different Omicron variants.

That’s good news for what we can expect from COVID-19 in coming years, at least if the variants remain in the Omicron family. But while we might be building hybrid immunity, the virus can still have negative effects. Other studies have shown that repeated infections can damage the brain, heart, and lungs—so avoiding infections in the first place is better for health in the long run.

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