The coronavirus is simply too widespread and too transmissible. The most likely scenario, experts say, is that the pandemic ends at some point—because enough people have been either infected or vaccinated—but the virus continues to circulate in lower levels around the globe. Cases will wax and wane over time. Outbreaks will pop up here and there. Even when a much-anticipated vaccine arrives, it is likely to only suppress but never completely eradicate the virus. (For context, consider that vaccines exist for more than a dozen human viruses but only one, smallpox, has ever been eradicated from the planet, and that took 15 years of immense global coordination.) We will probably be living with this virus for the rest of our lives…

At this point, how long immunity to COVID-19 will last is unclear; the virus simply hasn’t been infecting humans long enough for us to know. But related coronaviruses are reasonable points of comparison: In SARS, antibodies—which are one component of immunity—wane after two years. Antibodies to a handful of other coronaviruses that cause common colds fade in just a year. “The faster protection goes away, the more difficult for any project to try to move toward eradication,” Grad told me.

This has implications for a vaccine, too. Rather than a onetime deal, a COVID-19 vaccine, when it arrives, could require booster shots to maintain immunity over time. You might get it every year or every other year, much like a flu shot.