The omicron wave that assaulted the United States this winter also bolstered its defenses, leaving enough protection against the coronavirus that future spikes will likely require much less -- if any -- dramatic disruption to society.
Millions of individual Americans' immune systems now recognize the virus and are primed to fight it off if they encounter omicron, or even another variant.
About half of eligible Americans have received booster shots, there have been nearly 80 million confirmed infections overall and many more infections have never been reported. One influential model uses those factors and others to estimate 73 percent of Americans are, for now, immune to omicron, the dominant variant, and that could rise to 80 percent by mid-March.
This will prevent or shorten new illnesses in protected people and reduce the amount of virus circulating overall, likely tamping down new waves. Hospitals will get a break from overwhelmed ICUs, experts agree.
"We have changed," said Ali Mokdad, a professor of health metrics sciences at the University of Washington in Seattle. "We have been exposed to this virus and we know how to deal with it."
The coronavirus -- the current variant or future ones that are sure to pop up -- remains a dangerous germ. It is still infecting more than 130,000 Americans and killing more than 2,000 every day. Tens of millions of people remain vulnerable.
And there will be future outbreaks. The notion of a "herd immunity" that could stop the virus has slipped away under the harsh reality of new variants, waning immunity, and the rejection of vaccines by some Americans.
However, the coronavirus is no longer new. Two years ago, it arrived in a nation where nobody's immune system had seen it before. The entire population -- 330 million people -- were immunologically naive, that is, susceptible to infection.
"I am optimistic even if we have a surge in summer, cases will go up, but hospitalizations and deaths will not," said Mokdad, who works on the Institute for Health Metrics and Evaluation model, which calculated the 73 percent figure for the Associated Press.
With varying degrees of relief and caution, many Americans are starting to return to their pre-pandemic lifestyles.
Sarah Rixen, 41, of Bismarck, North Dakota, started singing again with a civic chorus after taking a year off. Now, with omicron winding down, she said she feels more confident than at any time since the crisis began.
"But I am still a little leery that there could be another variant around the corner," Rixen said, noting her family and most of her relatives are fully vaccinated. "I am still going to wear a mask."
As mask mandates ease, workers return to offices and flights fill up, experts are trying to understand whether this return to normal can last, or if another setback is looming.
To address that, researchers are trying to answer questions about the virus, the vaccine, and how our bodies respond: How fast is booster protection waning against omicron? How long does protection from infection last? How many mild infections were never reported? How many people got infected but had no symptoms?
To find clues, they use health data from other countries such as Britain, Denmark, South Africa and Qatar to project what could be in store.
Scientists at Johns Hopkins Bloomberg School of Public Health estimate about three out of four people in the United States will have been infected by omicron by the end of the surge.
"We know it's a huge proportion of the population," said Shaun Truelove, an epidemiologist and disease modeler at Johns Hopkins. "This varies a lot by location, and in some areas we expect the number infected to be closer to one in two."
That means different regions or groups of people have different level of protection -- and risk. In Virginia, disease modelers are thinking about their population in terms of groups with different levels of immunity.
They estimate about 45 percent of Virginians have the highest level of immunity through boosted vaccination or through vaccination plus a recent infection with omicron. Another 47 percent have immunity that has waned somewhat; and 7 percent are the most vulnerable because they were never vaccinated and never infected.
In all, the vast majority of Virginians have at least some immunity, said Bryan Lewis, a computational epidemiologist who leads University of Virginia's COVID-19 modeling team.
"That's going to be a nice shield of armor for our population as a whole," Lewis said. "If we do get to very low case rates, we certainly can ease back on some of these restrictions."
Still, while the population is better protected, many individuals are not. Even by the most optimistic estimates for population immunity, 80 million or so Americans are still vulnerable. That's about the same as the total number of confirmed infections in the U.S. during the pandemic.
"The 26 percent who could still get omicron right now have to be very careful," Mokdad said.
FILE - Registered nurse Jessalynn Dest, left, removes protective equipment and washes her hands after leaving a COVID-19 patient's room as speech therapist Sam Gibbs puts on safety clothing while preparing to see a patient in the acute care unit of Harborview Medical Center, Friday, Jan. 14, 2022, in Seattle. The coronavirus — the current variant or future ones that are sure to pop up — remains a dangerous germ. It is still infecting more than 130,000 Americans and killing more than 2,000 every day. Tens of millions of people remain vulnerable. (AP Photo/Elaine Thompson, File)
FILE - Pitt student Michael Burke, 21, gets a COVID-19 booster shot from nursing student Colette Sayegh, on Wednesday, Jan. 12, 2022, at the Peterson Events Center in Oakland, Pa. Millions of individual Americans’ immune systems now recognize the virus and are primed to fight it off if they encounter omicron, or even another variant. (Andrew Rush/Pittsburgh Post-Gazette via AP, File)
A customer enters a restaurant past a sign posted to the door requiring masks Wednesday, Feb. 9, 2022, in Providence, R.I. The omicron surge that’s still infecting more than 130,000 Americans every day in February 2022 will leave the nation with enough protection against the coronavirus that future spikes will likely bring much less — if any — dramatic disruption to society. (AP Photo/David Goldman, File)
FILE - People wait in line to test for COVID-19 on Wednesday, Jan. 12, 2022, in Long Beach, Calif. The coronavirus — the current variant or future ones that are sure to pop up — remains a dangerous germ. It is still infecting more than 130,000 Americans and killing more than 2,000 every day. Tens of millions of people remain vulnerable. (AP Photo/Ashley Landis, File)
FILE - A man walks underneath the marquee of the Alex Theatre in Glendale, Calif., which bears a message urging people to get COVID-19 vaccine booster shots, Monday, Jan. 24, 2022. The omicron wave that assaulted the United States this winter also bolstered its defenses, leaving enough protection against the coronavirus that future spikes will likely require much less — if any — dramatic disruption to society. (AP Photo/Chris Pizzello, File)