While the White House once targeted July 4 as the date that at least 70 percent of adults would be at least partly vaccinated, officials acknowledged last month that they would almost certainly miss that goal as the vaccination rate has plummeted from a peak in April.
And while 20 states, Washington, D.C., and two territories exceeded the 70 percent mark last week, the country’s progress as a whole has slowed significantly, with only about one million doses now being administered each week on average. On Sunday, roughly 67 percent of adults had received at least one shot, according to data compiled by The New York Times.
The rapid spread of the highly contagious Delta variant has also raised concerns among public health officials, who fear that new outbreaks could occur in parts of the country where vaccination rates have stayed comparatively low, and that the variant could mutate in ways that leave even vaccinated Americans vulnerable.
While the pageantry at the White House will present a display of normality that seemed far from likely at the beginning of Mr. Biden’s term, the occasion will be characterized by a sense of restraint rarely seen under the previous administration.
Even as new cases swelled toward a summer peak last year, President Donald J. Trump went ahead with a 35-minute fireworks display and military flyovers on the National Mall, against the wishes of Mayor Muriel E. Bowser of Washington, who urged people not to attend. The fireworks show this year will be only half as long, and Ms. Bowser, encouraged by progress on vaccines, has welcomed guests back to the city.
Under Mr. Trump, the White House hosted other large gatherings long before vaccines had been approved, including two celebrating the nomination and confirmation of Justice Amy Coney Barrett, in which he and several other attendees were believed to have been exposed and infected.
For Mr. Biden, the celebrations this year appear choreographed to signal that Americans can enjoy some degree of normality in coming together, even as his own public health officials have continued to stress the importance of maintaining momentum on vaccines.