• Centers for Disease Control and Prevention data shows the seven-day average of daily shots reported administered held above 3 million for the 12th straight day.
• The milestone comes as President Biden's deadline arrived Monday for states to expand vaccine eligibility to all adults.
• The nationwide level of daily new coronavirus cases remains elevated at an average of about 67,400, up 26% from last month's lows but down slightly from one week ago.

Centers for Disease Control and Prevention data shows 3.5 million vaccinations administered across the U.S. on Sunday. The seven-day average of daily shots given has held above 3 million for 12 straight days.

Half of all American adults have now received at least one dose of a Covid vaccine, according to the CDC. The milestone comes as President Joe Biden's deadline arrived for states to expand their vaccine eligibility requirements. Biden asked states to open appointments to all U.S. adults by Monday.

Biden said in a video posted to Twitter on Monday that states have met that deadline. He encouraged Americans to get the vaccine.

As of today, every American is eligible to receive the COVID-19 vaccine. For yourself, your neighbors, and your family — please, get your vaccine. pic.twitter.com/o75JYpGe6r

— President Biden (@POTUS) April 19, 2021

The nationwide level of daily new infections remains elevated at an average of about 67,400, up 26% from last month's lows but down slightly from one week ago.

U.S. vaccine shots administered

The United States is reporting an average of more than 3 million daily vaccinations administered over the past seven days, according to CDC data.

Johnson & Johnson vaccinations are still paused, after the Food and Drug Administration and the CDC advised states to temporarily suspend the use of the shot after six women developed rare but severe blood-clotting issues.

The U.S. has administered far fewer J&J shots than Pfizer or Moderna vaccines, but the one-shot option is valuable for certain situations and communities. Mass vaccination sites and mobile vans have an easier time with the Johnson & Johnson storage requirements, and administering a two-dose regimen can be a challenge in certain populations, such as prisoners who are changing facilities or homeless people who do not have a permanent residence.

U.S. share of the population vaccinated

On Sunday, the CDC reported that half of all U.S. adults have gotten at least one shot. Of those ages 65 and older, 81% have received one dose or more and roughly two-thirds are fully vaccinated.

Nearly 40% of the total U.S. population, including those not currently eligible for available vaccines, has received at least one dose of a Covid vaccine, CDC data shows, and more than 25% is fully vaccinated.

U.S. Covid cases

The seven-day average of daily new infections in the U.S. stands at about 67,400, according to data from Johns Hopkins University. That figure is up 26% from the country's most recent low of about 53,600 recorded in late March, but is down slightly from one week ago.

Dr. Scott Gottlieb, a former Food and Drug Administration commissioner, said Monday on CNBC's "Squawk Box" that he expects warmer weather and increased vaccination rates to lead to a decrease in case counts.

"I think we're going to start to see the pandemic roll over in the United States in terms of cases coming down," he said. "We're still going to have outbreaks in some parts of the country — we're never going to virtually eliminate this virus — but I think you're going to start to see cases come down quite dramatically as we get into May."

Gottlieb cited San Francisco as an example of where the country might be heading. The city reports 40% of adults are fully vaccinated, he said, and is seeing only about 30 new Covid cases per day.

U.S. Covid deaths

The U.S. is currently reporting 723 Covid deaths per day, based on Hopkins data.

On Saturday, the global Covid-19 death toll surpassed 3 million, larger than the population of Chicago and equivalent to Philadelphia and Dallas combined.

Disclosure: Scott Gottlieb is a CNBC contributor and is a member of the boards of Pfizer, genetic testing start-up Tempus, health-care tech company Aetion Inc. and biotech company Illumina. He also serves as co-chair of Norwegian Cruise Line Holdings' and Royal Caribbean's "Healthy Sail Panel."