The findings may help put to rest lingering fears that protection against the virus will be short-lived.
Researchers in both studies examined bone marrow in volunteers who had been exposed to the coronavirus about a year earlier. They found that a part of the immune system called "B cells" seemed to stick around, providing the body with a biological "memory" of a coronavirus infection.
The study published online at BioRxiv, a site for biology research, found that these B cells continued to grow and strengthen at least 12 months later.
The other study was published in the journal Nature Monday.
Health officials have emphasized for months that COVID-19 vaccinations turbo-charge the body's antibody response. In essence, a shot gives the body more antibodies than a natural infection would, and more antibodies are usually associated with longer protection, said Dr. William Schaffner, a professor in the Department of Health Policy at Vanderbilt University.
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Experts, however, have no way to definitely know now how long protection from coronavirus lasts, as the virus is new and therefore hasn't been studied over long periods of time. While the findings are optimistic, these studies also don't take virus variants into account, Schaffner said.
And just because the studies show evidence of long-lasting immune responses doesn't mean experts know how long complete protection lasts, said Dr. Dan Barouch from Beth Israel's Center for Virology and Vaccine Research.
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This means that despite promising results, booster shots may still be needed.
"I don't anticipate that the durability of the vaccine protection is going to be infinite. It's just not, so I would imagine we will need at some time a booster," Dr. Anthony Fauci, the nation's top infectious disease expert, said Wednesday during a Senate hearing.
ABC News contributed to this report.