Over the past nine months, vaccination has utterly transformed the shape of the pandemic in the places where it has penetrated the whole population. The effect isn’t just visible in countries like Portugal or Iceland — where the threat appears to be fast receding and which give an encouraging picture of our possible future — but in parts of the United States as well. But for all its transformative, liberating power, vaccination has not broken the basic age skew of the disease or offered anyone an exit ramp from it. Instead, in two profound ways, vaccination has confirmed the age skew: by producing severe breakthrough cases concentrated overwhelmingly in the elderly and by reducing the risk faced by individuals by an astonishing degree that is nevertheless smaller than the still more striking effect of age.

Although vaccines do substantially reduce the risk of infection, too, breakthrough cases are not terribly uncommon, accounting for perhaps as many as one-quarter of all new infections these days, as the CDC estimated in Los Angeles. But they are overwhelmingly mild, and in the rare cases when they do grow severe, they tend to be among the old and very old. According to the CDC, 70 percent of breakthrough cases resulting in hospitalizations and 87 percent of those resulting in death were in patients over 65. The median age of breakthrough deaths in England was 84; in King County, it was 79.

The second confirmation follows from the first and explains why, even given the power of vaccines, there are still some number of severe breakthrough cases and deaths. That 11-fold reduction of risk found in the national CDC study, for instance? Enormous, of course, but it is an average across the observed population as a whole and represents only the equivalent of the *difference between an unvaccinated 86-year-old man and a 61-year-old one, all else being equal. According to an analysis of British data by the Financial Times, a vaccinated 80-year-old has about the same mortality risk as an unvaccinated 50-year-old, and an unvaccinated 30-year-old has a lower risk than a vaccinated 45-year-old. Even a 42-fold reduction, as was found in King County, would only be the rough equivalent of the difference between an unvaccinated 85-year-old woman and an unvaccinated 50-year-old