Persuading vaccine holdouts among the elderly at this point is hard, but COVID risk is so high for this group that it’s very much worth trying. Boosting the already vaccinated, by contrast, should be eminently doable, as the group is clearly open to vaccines. With America’s vaccination campaign sputtering, this is where efforts are likely to have the biggest payoff. Hospitalizations and deaths are so heavily concentrated in older people, in fact, that a single course of a vaccine in someone over 65 might have the same effect on those numbers as dozens given to the young. The U.S. fortunately has enough vaccine doses that we don’t have to choose whom to vaccinate. But as immunity in the unboosted continues to wane and persuading new people to get immunized becomes harder, a focused effort on vaccinating and boosting the elderly can have an outsize impact on preventing hospitalizations and deaths in the next COVID wave. The most severe COVID outcomes are not the only ones worth preventing, but they are the most urgent if we don’t want hospitals and morgues filling up again.

Consider the current Omicron wave, which has been far deadlier in the U.S. than in other highly vaccinated and boosted countries. The U.S. has reached 80 percent of its pre-vaccine peak in daily deaths, compared with only 20 to 30 percent of peaks reached in other countries. America has not only a lower overall vaccination rate but lower coverage in the elderly. England, for example, has achieved 96 percent full-vaccination coverage in people over 65. In the U.S., this number is 88.5 percent, with big geographic variations that range from 79 percent in Arkansas to 95 percent in Vermont.

These percentages may all look high, but they represent very different levels of remaining risk. “People see 90 and 95 percent as not very much” of a difference, says Adam Kucharski, an infectious-disease modeler at the London School of Hygiene and Tropical Medicine. He prefers to invert the number. “Think of it as: There’s 5 percent unprotected or 10 percent unprotected.” That doubles the pool of people over 65 who are at high risk for hospitalization and death. In a massive epidemic wave like that of Omicron, hospitalizations and deaths can scale up very quickly.