Vaccination rates have been rising steadily in recent weeks as fear of the Delta variant has grown. Providers were administering about 837,000 shots a day late last week, and Mr. Biden said the most recent seven-day total was the highest since early July. He said more people in Alabama, Arkansas, Louisiana and Mississippi — some of the states with the highest caseloads — got their first shots in the past month than in the previous two months combined.
Dr. Marks said that myths about the vaccines remain a major impediment to fighting the pandemic, including false claims that shots would cause infertility, would foster rather than prevent Covid-19, and had even led to thousands of deaths.
“Let me be clear: These claims are simply not true,†he said.
The F.D.A. is in the midst of a blizzard of decisions about coronavirus vaccines. The next major one looming is whether to authorize booster shots.
The Biden administration said last week it planned to offer third shots to adults who got the Pfizer and Moderna vaccines, eight months after their second injection, starting Sept. 20. Third shots are already authorized for some people with immune deficiencies, but the risk-benefit calculus is different for the general population.
Federal health officials said that both Pfizer’s and Moderna’s vaccines, which rely on similar technology, wane in potency over time. That trend, they said, is converging with the rise of the particularly dangerous Delta variant, making those who completed their vaccinations at the start of the year increasingly vulnerable to infection.
Some public health experts have challenged the plan for booster shots as premature. They say the available data shows that the vaccines are holding up well against severe disease and hospitalization, including against the Delta variant. Extra shots would be warranted only if the vaccines failed to meet that standard, some have said.
Regulators are still reviewing Moderna’s application for full approval of its vaccine, which it filed in June, a month after Pfizer. That decision could take several weeks. Johnson & Johnson is expected to apply for full approval soon.
Susan C. Beachy and Coral Murphy Marcos contributed reporting.
