Eventually, the virus could become a much milder illness—but for now, vaccination and surveillance are critical to end the pandemic phase.

AS COVID-19 CONTINUES to run its course, the likeliest long-term outcome is that the virus SARS-CoV-2 becomes endemic in large swaths of the world, constantly circulating among the human population but causing fewer cases of severe disease. Eventually—years or even decades in the future—COVID-19 could transition into a mild childhood illness, like the four endemic human coronaviruses that contribute to the common cold.

“My guess is, enough people will get it and enough people will get the vaccine to reduce person-to-person transmission,” says Paul Duprex, director of the University of Pittsburgh’s Center for Vaccine Research. “There will be pockets of people who won’t take [the vaccines], there will be localized outbreaks, but it will become one of the ‘regular’ coronaviruses.”

But this transition won’t happen overnight. Experts say that SARS-CoV-2’s exact post-pandemic trajectory will depend on three major factors: how long humans retain immunity to the virus, how quickly the virus evolves, and how widely older populations become immune during the pandemic itself.

Depending on how these three factors shake out, the world could be facing several years of a halting post-pandemic transition—one marked by continued viral evolution, localized outbreaks, and possibly multiple rounds of updated vaccinations.