President Biden is 79, and Americans his age and older have made up larger and larger shares of those dying from Covid in recent months. The virus has taken advantage of falling immunity caused by the time elapsed since many older people’s last vaccinations, and the Omicron variant has evolved a growing ability to skirt the body’s defenses.

Covid has been killing substantially fewer Americans of all ages this summer than it did during the peak of the wintertime Omicron wave. Still, older people remain at significantly higher risk.

As of early June, four times as many Americans ages 75 to 84 were dying each week from the virus compared with people two decades younger, according to data from the Centers for Disease Control and Prevention. (Those death counts are provisional, the C.D.C. cautioned, because they were based on death certificates and did not account for all deaths in those age groups.)

That is an even bigger age gap than existed at the peak of the Omicron wave this winter. Then, the number of people aged 75 to 84 killed by Covid each week was twice as high as the number aged 55 to 64.

The president received a second booster shot in late March, significantly reducing his risk of severe illness. This spring, people 50 and older who had received a single booster were dying from Covid at four times the rate of those with two booster doses, the C.D.C. has reported.

In 2022, Covid deaths, though always concentrated in older people, have skewed toward older people more than they did at any point since vaccines became widely available. Many older people were vaccinated early in 2021, and among those who have not yet received a booster shot, immune defenses generated by the shots have significantly waned.

In contrast, middle-aged Americans, who suffered a large share of pandemic deaths last summer and fall, are benefiting from greater stores of immune protection from both vaccination and prior infections.

While Covid deaths remain far lower than in the winter, they are climbing again among older people as the immune-evasive Omicron subvariant known as BA.5 causes more infections, according to the latest C.D.C. data. From early May to early June, the number of Americans ages 75 to 84 dying from Covid each week increased by nearly 50 percent.