December 21, 2021 1:21 PM EST

For most of 2020, avoiding the novel coronavirus was at the heart of almost every piece of public-health advice. Then, vaccinations largely gave Americans their lives back. Breakthrough infections were remarkably rare in the early months of mass vaccination. Only about 10,000 people—or 0.01% of the 101 million U.S. adults who had been fully vaccinated—reported one by the end of April 2021, illustrating that post-vaccine infections were possible, but unlikely.

That changed when the more contagious Delta variant began spreading over the summer and sickening more people who’d had their shots. Now—though vaccinated people remain far more protected than those without their shots—the highly transmissible Omicron variant may force a complete rethinking of breakthrough infections.

Rare no longer

A lot remains to be learned about Omicron, but the U.S. Centers for Disease Control and Prevention (CDC) has warned that it is likely to cause breakthrough infections. Early studies suggest COVID-19 vaccines will continue to dramatically limit severe disease and death, but may not be as good at preventing symptomatic disease caused by Omicron, compared to other strains. The variant also arrived at an inopportune time, when vaccine-related immunity was starting to wane for people who had gotten their shots early in the year and hadn’t yet been boosted.

New York City, one of the first places in the country to experience a significant Omicron spike, is recording an average of more than 7,000 cases per day, despite 71% of the city’s population being fully vaccinated and about 1.7 million people receiving boosters. As of Dec. 4, the case rate among fully vaccinated New Yorkers was 97 per 100,000 people—far lower than the 804 cases recorded per 100,000 unvaccinated people, but roughly double the rate observed among vaccinated people a month earlier.

“Even in quite vaccinated parts of the country, [we should expect to] break records in the numbers of new daily cases confirmed because of Omicron,” says Anna Bershteyn, an assistant professor of population health at the New York University Grossman School of Medicine.

COVID-19 vaccines weren’t built to stop all infections, but rather to stop those infections from turning severe or fatal. They’re still doing that job very well, which should relieve the 61% of Americans who are fully vaccinated—and particularly the 30% of that group who have received a booster. Recent studies suggest that booster shots greatly increase antibody levels.

But even though breakthrough infections may pose minimal risk to millions of vaccinated individuals, they are still dangerous for the U.S. as a whole. Almost 40% of the population, including all children under 5, remains unvaccinated, and millions of immunocompromised, elderly and medically vulnerable people are still at higher-than-average risk. Plus, our health care networks have been overstrained for almost two years, and any extra burden could prove disastrous.

“We look at COVID as an individual disease that affects an individual person when infected,” says Nir Menachemi, a professor of health policy and management at the Indiana University School of Public Health. But “it’s also a disease that affects a population.”

Protecting a fragile health care system

Now that the world has largely reopened and a new, highly contagious variant is here, avoiding COVID-19 completely is no longer a realistic long-term plan, says Dr. Megan Ranney, an emergency medicine physician and associate dean of Brown University’s School of Public Health.

“There is a high likelihood that most of us will catch COVID at some point,” Ranney says. “The goal of the vaccines is to delay that as long as possible, and then to make it so that, if and when we do catch COVID, it is as mild as possible.”

But that doesn’t mean we should abandon every precaution, Ranney says. For one thing, we’re still learning a lot about what Omicron can do. There are also unanswered questions about how often breakthrough infections lead to Long COVID and whether Omicron changes those odds.

But arguably the most pressing issue, she says, is strain on the health care system, which has been overburdened for almost two years. “Our system has no slack right now,” Ranney says. “An extra 10 or 20 hospitalizations is having the same effect on the system as an extra 50 hospitalizations had a year ago.”

COVID-19 vaccines work so well that only a small percentage of breakthrough infections are likely to lead to severe disease. But Omicron is capable of causing such large spikes in cases that even a small percentage could translate to a relatively large number of people—potentially more than the system can handle, particularly on top of all the unvaccinated people likely to get sick.

Based on her projections, Bershteyn says hospitals in highly vaccinated areas of the country should be able to handle the coming Omicron wave, while those in less-vaccinated regions may be in for bigger surges. In any area, though, hospital staffing could become a problem if large numbers of medical professionals get sick at once, she says. Already, many medical centers are operating with skeleton crews, in part due to high rates of burnout and resignation. And that means care is in jeopardy across the board—not just for COVID-19 patients, but also for people who need to be treated for injuries, strokes, heart attacks and other emergencies.

More infections=more precautions

To get past the Omicron surge, all Americans need to once again aim to flatten the curve—this time, with the help of vaccines, boosters and rapid tests, as well as masks, physical distancing and ventilation. Policymakers can guide this process by implementing mask and vaccine mandates, improving access to tests and shots and setting standards for things like building ventilation. Ranney says we also have to start rebuilding health care capacity by tapping the U.S. Public Health Service Commissioned Corps and National Guard, and by quickly training people to fill non-physician vacancies.

But there’s a long way to go. In addition to overtaxed hospitals, testing centers in many parts of the country are overwhelmed and at-home rapid tests are hard to come by and expensive. “It’s the same problem we had back in March of 2020,” Ranney says. “If you can’t test people and tell them whether or not they have COVID, then you can’t tell folks who needs to stay home.”

Without that ability, people in areas where the virus is spiking may need to return to more sweeping precautions. The lockdowns of 2020 are unlikely to come back, but measures like indoor masking and avoiding big crowds may be necessary, at least temporarily.

“We need to do what we can to flatten the curve,” says Dr. Rebecca Wurtz, an infectious disease physician and associate professor of health policy and management at the University of Minnesota School of Public Health. “I’m thinking it’s going to be 10 weeks, 12 weeks until we’re able to relax a little bit and move into a normalized response.”

Living with COVID-19

By a “normalized response,” Wurtz means that, eventually, COVID-19 breakthrough infections may be treated like “any other respiratory viral infection.”

Right now, someone with a breakthrough case of COVID-19 is supposed to isolate for 10 days after testing positive or developing symptoms, even though recent evidence suggests that vaccinated people may clear the virus faster. Before too long, she says, we’ll probably scrap that policy and move toward a more familiar approach, in which people stay home while they’re symptomatic but don’t necessarily pause their entire lives for 10 days. Someday, people may not even need to test or seek treatment, so long as they only have mild symptoms, Wurtz says.

Wurtz emphasizes that we’re not ready to abandon preventive tactics yet, given the number of people who remain vulnerable to the virus, the strain on our health care systems and the unanswered questions about Omicron, including its relationship to Long COVID and other serious outcomes.

But once we get past the Omicron surge, how do we transition into treating COVID-19 as a normal part of life?

In the long term, policymakers should focus on addressing many of the socioeconomic problems that allowed COVID-19 to flourish, like inadequate access to health care and safe housing, says Menachemi. The public also needs better communication about “why everyone’s effort contributes to us returning to normal” and clearer guidelines for when certain restrictions are or are not required, he says.

As the population-level threat of COVID-19 stabilizes, our individual view of breakthrough infections is likely to change from something scary to something unfortunate but, ultimately, routine, Menachemi says.

“We need to start preparing people for the understanding that they will probably, at some point, get COVID,” he says, “and if they’re vaccinated and up to date on their boosters, it’s probably not going to be a big deal.”

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Write to Jamie Ducharme at jamie.ducharme@time.com.

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