“I want to move on, too,” said Colledge, 70, of Salt Lake City. “It’s kind of confusing for me because I feel like, ‘What about me? Why am I safer now than I would’ve been, I don’t know, three months ago?’ ”

The unsettling answer for Colledge is that her risk continues to be dangerously high because of her illness, even though transmission of the coronavirus has dropped significantly. Which means she must now do a risk-benefit calculus for every journey outside of her home. But for many other Americans, there was palpable relief on Feb. 25, when the CDC shifted the vast majority of U.S. counties from red — signaling high transmission — to green, meaning low levels of disease and no need to mask indoors.

The changes were based on a new framework designed to protect communities from the worst — a surge so big that it might overwhelm local hospitals — while being less disruptive to everyday life, amid plummeting case counts and a weary public’s desire for relief from masking and other public health measures. But some worry it leaves the country unprepared for another wave and abandons those who are most vulnerable. The plan’s adequacy may soon be tested if the United States sees the same sharp increases in coronavirus cases now bedeviling Europe — a possibility Biden officials are anticipating. If such increases lead some U.S. communities to be reclassified as red, it remains an open question whether state and local officials would be willing to reinstate controversial indoor masking guidelines. There may be little political appetite for such measures, even in Democratic areas.

“Convincing a large swath of the population to put masks back on will be very difficult,” said Nirav Shah, director of Maine’s Center for Disease Control and Prevention.

For an administration that has vowed to “follow the science,” navigating a return to normalcy in the pandemic’s third year is an inherently messy and uncertain process. Federal health officials have developed new metrics, based on previous coronavirus waves, that will anticipate the burden of severe disease on local hospitals by incorporating county-by-county data on covid-19 hospital admissions, as well as case counts. But there are no clear-cut steps to a new pandemic normal — only judgment calls that will have to be continuously adjusted, depending on how an unpredictable virus mutates, said several senior administration officials and outside experts.

“There’s tons of trade-offs … and it’s a messy business,” Eli Perencevich, an infectious-disease physician at the University of Iowa, said of the effort to navigate a return to pre-pandemic life. “But I do think CDC is, you know, trying their best in a very, very continuously difficult situation. There’s no policy that’s going to please everybody.”

Some experts worry the new framework moves the burden of protection almost entirely to individuals, particularly those who are most vulnerable, including the immunocompromised and families with children too young to get vaccinated. Others wonder whether the agency’s new metrics will alert communities in time to take action to avert future surges, especially if they face variants with more immune evasion and severity than omicron or its cousin, BA.2, now fueling cases in Europe. Whether officials will act if they have sufficient notice is another question.

“I’m especially concerned about what seems to me to be a high hospitalization threshold for triggering implementation of community measures like indoor masking,” Jeffrey Duchin, health officer for Seattle and King County in Washington state, said in an email, noting the CDC’s triggers are equivalent to twice the highest weekly hospitalization rates for influenza over the past 12 seasons.

“As a trigger, waiting for this level of hospitalizations to implement measures to interrupt COVID-19 transmission may be too late,” he said.

U.S. is far better prepared

Several experts heralded the new guidelines and said they were appropriate as cases drop, especially given the nation’s broad immunity. For most people who are vaccinated and boosted, the coronavirus is unlikely to result in severe infection, hospitalization or death, even though some immune protection wanes after a few months. Experts and administration officials note the picture in March 2022 is far different from March 2020, with access to coronavirus vaccines, treatments and tests; N95 masks that offer one-way protection; and a better understanding of the virus.

“I acknowledge how this pandemic has disproportionately affected certain communities, whether they are vulnerable by virtue of where they live and work, or by virtue of coexisting disease,” CDC Director Rochelle Walensky said in an interview. “The benefit of where we are now compared to a year ago is that we have a whole host of things we can do with and for people,” including widespread testing and vaccination.

Yet as the United States and the world have learned repeatedly, there is no guarantee cases will remain low when the virus is still circumnavigating the globe, creating hot spots in parts of Asia and Europe that in the past have preceded outbreaks in the United States.

When CDC released the new metrics, Walensky said they could be dialed up or down if an evolving virus posed new challenges. Agency officials implied, but did not state forcefully, that another large surge would mean a return to indoor mask recommendations.

The effectiveness of the new metrics, as well as officials’ willingness to act, could be tested soon amid signs that the level of virus in wastewater is ticking up in New York City, California, Colorado, Florida, Ohio, Maine and West Virginia — although it is not yet clear whether cases and hospitalizations will follow suit, as they have in parts of Europe and Asia.

“Science doesn’t provide all the answers,” said Richard Besser, president and chief executive of the Robert Wood Johnson Foundation and a former acting CDC director. “The frustration that people are feeling — this sense that [some] people are feeling liberation and joy and others are feeling a sense of fear and abandonment — I totally get that and expect that’s how it’s going to be for some time until this pandemic does hopefully one day recede.”

Ringing alarms ‘when we really need to’

In much of the country — particularly states and cities led by Republicans — mask mandates fell away long ago. But in February, a number of Democratic governors began announcing an end to their mandates, well before the CDC updated its metrics.

The agency was in regular discussions with state health officials about what the rapid drop in cases meant and how to navigate the next phase of the pandemic. Despite polls showing the majority of Americans still favored some restrictions, including mask mandates, state and local leaders said their residents were growing restive. They wanted guidance from the CDC to help determine when mandates could be relaxed and when they might need to be reinstated, one senior administration official and two state health officials said. State officials said they asked that their hospitals’ capacity be included. These officials, along with others in this story, spoke on the condition of anonymity because they were not authorized to speak on the record.

Given the omicron variant’s transmissibility, almost the entire country’s map was still red even as the surge was waning toward the end of February. The CDC’s metrics were still based on case counts and test positivity. But many infections go undetected because people have no symptoms or do not seek treatment for mild symptoms. In addition, the results of rapid at-home tests are often not reported in official case counts. At the same time, many experts had been pushing for measurements of disease severity because the vast majority of those who were vaccinated — and especially those who received booster doses — would have mild or asymptomatic disease, according to three people familiar with the conversations.

Under its previous metrics, CDC was “ringing the alarm constantly throughout the pandemic, saying transmission is high, transmission is high, transmission is high,” said a senior CDC adviser. “But [it] didn’t mean anything. [Current metrics] … allow us to ring the alarm when we really need to. And to turn the alarm off when things are a little better and give people a break from the siren.”

Implicit in the latest guidance is this basic fact: The country is “at the point where we’re not able to prevent transmission from the virus from occurring,” said Aubree Gordon, an infectious-disease epidemiologist at the University of Michigan. “The severity of infection has dropped. A huge part of that is because of population-level immunity. I do think it’s appropriate guidance for the moment we are in now.”

With that in mind, officials “really thought through what is it that matters right now in this pandemic. And while cases are important, really, what we are most concerned about was medically significant disease,” the senior CDC adviser said.

They wanted to be able to predict “when our hospitals are going to fill up, when our ICU beds are going to be full, and when are we going to see an increase in the risk of death in the community from covid-19. Those are the things that really mattered. We wanted to predict those.”

Officials spent weeks identifying new metrics and then validating that they would accurately predict the impact on health-care systems three weeks later. They sought indicators that were available at the county level, reported at least weekly, and directly reflected the goal of minimizing severe disease or strain on the health-care system, according to a CDC scientific brief posted a week after the new guidance was released.

Death rates, for example, were not used because they lag new infections by weeks. Emergency-department visits for covid-19 and wastewater surveillance would be good early-warning systems, but data is not available for the whole country, so they were not included.

One new hospital metric — covid-19 cases per 100,000 population in the past seven days — is important early in a surge to signal anticipated health-care strain, the CDC scientific brief said.

But some people are pessimistic the new metrics will alert communities in sufficient time to reinstate measures like indoor masking to avert surges. New hospital admissions lag infections by at least a week, and by that time, a community could have significant amounts of disease.

The new metrics are of greater use “on the downside of a surge than on the upside,” said Andrew T. Pavia, a professor of pediatrics and infectious diseases at the University of Utah. “We need sensitive indicators to allow us to institute control measures when a new surge is beginning, not just to tell us when it is reasonable to stop them.”

Administration officials acknowledge the metrics are not perfect but believe they will sound alarms in time. Two senior administration officials said in a country as large and diverse as the United States, it’s difficult to get to a recommendation that makes sense for every state or county. In the end, they acknowledged, the new framework is a combination of science and judgment calls.

Figuring out when to reinstate prevention measures will also require judgment, the senior CDC adviser said.

“When should you ask people to put on a mask? When should communities consider screening testing? When should schools think about test-to-stay programs? Those types of prevention measures are really hard to model” and there is no precise number, backed by evidence, indicating when you should implement each measure, the adviser said. “That’s where I think policy came in and where judgment came in.”

Biden officials noted that even before they unveiled their framework and officially withdrew masking guidance for much of the country, many people had stopped wearing face coverings. Studies have shown cloth masks do not offer sufficient protection, and mandates had not specified what types of masks people should be wearing.

None of which is any consolation to Jacki and Ken Churchill, who fear for his survival. Ken, 52, has an immune deficiency that has prevented his body from producing antibodies since childhood. The couple continue to order groceries online, avoid eating out and home-school their 14-year-old son.

Mask mandates in their corner of Alaska, outside Anchorage, had afforded some peace of mind on Ken’s rare trips to doctor appointments. Not anymore.

“We’re just left to protect ourselves,” said Jacki, 51, a cardiac nurse who is preparing to fly to Maine to help care for a sick family member. She worries that if she should pick up an infection at an airport or on a plane, that could prove deadly for Ken. To plan for her 14-hour journey, she plans to “scarf down pre-packed food” in the open spaces where dogs are walked during her long layovers.

“We’re not trying to dampen anybody’s party,” Jacki said. “We’re just trying to live.”

Dan Keating contributed to this report.