Some public health experts hope that Americans will welcome the new shot as they would a flu jab. But demand for the vaccine has dropped sharply since 2021 when it first became available and more than 240 million people in the U.S., or 73% of the population, received at least one shot.

In the fall of 2022, by which time most people had either had the COVID virus or the vaccine, fewer than 50 million people got the shots.