Some individuals are getting “superhuman” or “bulletproof” immunity to the novel coronavirus, and experts are now explaining how it happens.

Per NPR, a series of new studies have found that some people gain “an extraordinarily powerful immune response” to the novel coronavirus, which causes COVID-19.

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These people produce a lot of antibodies. But they also create antibodies that can change quickly and are “capable of fighting off the coronavirus variants circulating in the world but also likely effective against variants that may emerge in the future,” according to NPR.

For example, one study found that individuals created antibodies that could stop six variants of concern all at once, including the delta variant. These individuals could also stop other coronaviruses.

Paul Bieniasz, a virologist at Rockefeller University who helped lead the research for several of these studies, told NPR that these individuals will have good luck in the future with more variants.

“One could reasonably predict that these people will be quite well protected against most — and perhaps all of — the SARS-CoV-2 variants that we are likely to see in the foreseeable future,” he said.

However, there’s a catch. Many of these individuals were infected with the novel coronavirus and then got the mRNA COVID-19 vaccine earlier this year. So the individuals had protection from the virus and then experienced a strong response to the vaccine.

Indeed, previous research backs up this theory. For example, recent real-world U.K. data suggests that protection from the delta variant “was higher when people had previously caught COVID-19” after they had been vaccinated, too, researchers said. Of course, the researchers still suggested people get the COVID-19 vaccine to stay safe from the coronavirus.

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But don’t go out searching for the coronavirus just yet. It would be “completely irresponsible” for people to get COVID-19 on purpose after they’ve gotten vaccinated since they can still end up hospitalized from the virus, the study’s lead author Sarah Walker told Business Insider.

And it doesn’t help that no matter your immunity levels, you can still spread the virus.

“While vaccinations reduce the chance of getting COVID-19, they do not eliminate it,” the researchers said.