But it does mean that what has long been the dream of most Americans enduring the pandemic — a point at which “all of this is over” and we go back to “normal,” with 2020 an aberrant year and COVID-19 as much a historical artifact for us as, say, SARS is in East Asia — may never come to pass precisely as imagined. Instead, in the medium term and perhaps even the long term, a likelier endgame is one in which large portions of the population are protected, from at least severe disease produced by at least some variants of the disease, but, with immunity falling short of the herd threshold, the disease continues to circulate — infecting even some of those who’ve been vaccinated, threatening the lives of those who haven’t, and continuing to evolve as it circulates, perhaps in some scary ways. For most of those who’ve received a vaccine, the disease will fade into the background a bit, joining the ranks of other endemic diseases, but as a social fact the coronavirus will remain — still a lethal threat to the unvaccinated and perhaps even a small slice of the vaccinated, and always a threat to evolve in ways that could make it more transmissible, or more lethal, or threaten immune protection.

What will that world look like? In Denmark, they are already planning on issuing immunity passports, which would allow those who’ve been vaccinated to travel and socialize and do business in ways that others still can’t — a sort of immunity apartheid system of the kind that many warned about at the beginning of the pandemic but appears more and more difficult to avoid and that may ultimately persuade some number of vaccine skeptics to receive doses after all. There could also be harder measures taken, with companies requiring vaccine compliance from employees or even a national vaccine mandate — though each of these measures would run up against health-privacy protections in the U.S., where even masking regulations have proved difficult to enforce. The fate of those measures of vigilance is unclear, too — if less than half of nursing-home workers are vaccinated, will long-term-care residents and staff be required both to mask up and to social distance in an ongoing way, as they have for the last year, in circumstances described as solitary confinement, which may have already produced a mental-health crisis? Especially in places with low vaccination rates, schools may deploy temperature checks and rapid spit-tests — or may disregard those protocols and risk sporadic outbreaks. And any time a new strain arises, in the American reservoir or abroad, there may be renewed panic and vigilance — with even already-vaccinated people waiting those many months it will take to roll out a tweaked vaccine to feel truly safe again.