After three months of vaccination across the U.S., a majority of American adults have gotten shots, and the effort will soon shift from mass inoculation to mop-up.

As of Saturday, 138.6 million people in the U.S. have received at least one COVID-19 vaccine shot. About 1.3 million more are getting a first dose every day, according to the Centers for Disease Control and Prevention. While the rate of new vaccinators is declining, even if were immediately cut in half, it would mean that six weeks from now more than half of the population of the U.S. and its territories will have had a dose.

Almost all of those who get a first dose are likely to their second, according to one CDC study. On top of that, more than 80% of people age 60 or over — the most vulnerable group — have had a dose and will likewise complete vaccination.

That may be sufficient, at least to see a significant impact on U.S. caseloads. The U.S. is currently about where Israel’s vaccine campaign was in mid-February, three weeks before cases there began to plunge. (Israel has, in total, vaccinated just under 60% of its population.)

But in the next few weeks, what the vaccine campaign is going to look like is going to change dramatically. The Biden administration is pursuing a strategy of abundance, which the White House has referred to as an “overwhelm the problem” approach. That means that there will likely still be widespread shipping of vaccines to pharmacies and health centers, inoculation clinics and mobile vaccine resources.

But what’s likely to disappear are lines and scarcity.

“It’s OK if there’s not a long line of 1,000 people,” Natalie Quillian, the White House’s deputy coordinator of its COVID-19 response, told Bloomberg. “That’s good, that was the plan.”

There are many signs that’s already happening. In New York City, which had some of the tightest vaccine availability at the start of the rollout, the health department announced Friday that appointments were no longer needed at city sites and people could walk in for shots.

All of this points to a U.S. mass vaccine campaign that’s closer to the end than the beginning.

For more than three months now, the Bloomberg Vaccine Tracker has published a daily figure of how many doses were reported administered in the U.S. After months of mostly going up, that figure is now starting to decline. The goal of a vaccine campaign is to run out of people to vaccinate. That’s where the country is now headed.

That doesn’t mean an end to the vaccine efforts; it just means that they look different. Jeff Zients, the White House’s COVID-19 response coordinator, said on Friday that the vaccine campaign is entering its “next phase.”

“Going forward, we expect daily vaccination rates will moderate and fluctuate,” he said at a briefing in Washington. “We’ve gotten vaccinations to the most at-risk and those most eager to get vaccinated as quickly as possible. And we will continue those efforts, but we know reaching other populations will take time and focus.”

It also means that how the vaccine rollout has been measured so far will be different. There will likely be no more days of 4 million doses administered. On Saturday, the U.S. tallied 3 million doses administered, the lowest Saturday total since March 20. Success will mean chipping away at the increasingly small group of people who haven’t gotten a shot yet. If that effort is working, the daily vaccine rates should continue to fall as health workers run out of people who need to be vaccinated.

It also means a looser supply chain.

The U.S. is now reasonably assured of having enough vaccine. It has contracted for 600 million shots from Pfizer Inc. and Moderna Inc., and the drugmakers are delivering those doses faster than they are being used. About 28 million shots are being shipped a week, and 21 million are being used.

Johnson & Johnson’s one-dose vaccine, which was on a brief safety hold after concerns about rare blood clots, is likely to end up an also-ran in the U.S. Given how much Pfizer and Moderna is being shipped versus how much is being consumed, J&J’s shot may end up as a comparatively niche product, or be used mostly abroad, or reworked as a booster shot.

There are just under 10 million J&J doses that have been delivered but are still unused, according to CDC data. At the current rates of delivery and use of Moderna’s and Pfizer’s shots, about 7 million doses a week of those vaccines are building up, as well.

Measuring the vaccine rollout in May the way it was measured in March gives the wrong picture. In the early days of the rollout, having 7 million doses a week go unused would have been a failure. Now it’s more of a necessity. If you want to get to hard-to-reach, potentially reluctant people, you need to make it easy for them. That means lots of vaccine on standby, sitting around on a shelf.

But it doesn’t make for a razor-thin supply chain. Bloomberg has tracked the percentage of shots used over the course of the U.S. effort. At the peak of demand, some states were reporting that well over 90% of every dose delivered to them was being used, often within a few days of delivery.

Those days will disappear, and those use-ratios will fall. Mass-vaccine clinics filled with eager shot-seekers are great at injecting every last dose at the start of a rollout. They’re far less useful in attracting what one of Maine's top health officials, Nirav Shah, referred to this week as the “not able,” the “not right now” and the “not ever.”

Reaching those remaining people will be more of a steady grind. Many may get a dose at a doctor’s office during a visit for another condition. Others will be vaccinated at work, at a mobile clinic, or when they get another scheduled vaccination, like a flu shot.

But those efforts are likely to begin to fade into the background hum of the day-to-day operations of U.S. health care. Public health can go back to being boring again.

The start of the vaccine campaign was like a blockbuster movie that millions of people saw in theaters (remember those?).

Now we’re heading for the phase when the people who missed it on the big screen are streaming it at home: Oh, you finally got your shot? Yeah, I got it when it came out.