It's estimated that nearly 60 million Americans have dodged getting COVID-19. Many studies are being done to find out why.

"For one thing, a lot of the people who think they haven't had COVID may have and just were not symptomatic, so we've been focused on those people,” said Jill Hollenbach, a professor of neurology at the University of California at San Francisco.

While there are studies looking into why some people have never been infected, Hollenbach studied why some people infected with COVID-19 never become ill.

"What about those people who we know have been infected, they've had a positive test for COVID, what about those people who never get any symptoms at all,” Hollenbach added.

Hollenbach says between 10 and 30 percent of people infected with COVID will be asymptomatic. Her team found the answer has to do with genetics. They discovered a mutation that keeps people from developing COVID symptoms, even though they have the virus.

"A certain version of these immune response genes, HLA, this is a very common version of this gene many people have seems to be really important in helping people have this asymptomatic disease course,” she said.

Hollenbach says the research is so new, they're still working to get it published. She hopes it will lead to further advancements in treatment and vaccines.