April 29, 2022 1:12 PM EDT

They were the words everyone has been waiting to hear—that the COVID-19 pandemic is dialing down from the five-alarm fire that flared up in 2020 to a somewhat lesser conflagration. On April 27, the U.S.’s chief medical advisor, Dr. Anthony Fauci, described the country as in a “transitional phase, from a deceleration of the numbers into hopefully a more controlled phase and endemicity” in an interview with the Washington Post.

His comments come almost two years to the day after pharmaceutical manufacturers shipped the first batches of their COVID-19 vaccines for early testing. Fauci noted that those vaccines, as well as drug treatments that can control the virus in infected people, are largely responsible for the fact that the initial urgency of the pandemic as a public health threat is over. But COVID-19 itself isn’t quite finished with us. The virus continues to mutate, and the latest variations being reported out of South Africa—new subvariants of Omicron including BA.4 and BA.5—are sobering reminders that the virus isn’t standing still.

“Pandemic” vs. “Endemic”

Although we may be out of the urgent pandemic phase, we’re not quite ready to call COVID-19 endemic, which would mean the virus is still among us but relatively under control, similar to influenza.

And it’s not clear when that will happen. Even if it does, health experts may not all agree about the transition. There are no hard and fast definitions for “pandemic” and “endemic,” and no thresholds for case numbers or deaths that mark a shift from one to the other. The World Health Organization considers a pandemic to be an “epidemic occurring worldwide, or over a very wide area, crossing international boundaries and usually affecting a large number of people.” Experts have noted that these parameters say nothing about how quickly the outbreak is spreading, how much disease it’s causing, or what role immunity in the population plays.

But those are the factors that are critical for public health experts and political leaders as they manage a pandemic. There are no metrics for determining when to dial down an initial urgent response, or to pull back on drastic measures such as lockdowns and mask mandates.

That’s what the world is grappling with now—figuring out whether the risk of SARS-CoV-2 is now at a point where we can treat it more like influenza, by protecting ourselves as much as we can with immunization and basic hygiene such as washing our hands and covering our coughs, or whether we still need to manage SARS-CoV-2 as a serious enough threat for most people that we should maintain public health measures such as mask-wearing and social distancing.

Read more: Most Americans Have Had COVID-19. That Doesn’t Mean They Won’t Get It Again

What a “controlled pandemic” looks like

Fauci argues that we are somewhere in between those two situations, describing our current status as a “controlled pandemic”—not quite the urgent threat of a pandemic, but again not quite ready for the ease of mind that comes with being in an endemic phase of an outbreak. And the numbers support that: Since the beginning of the year, cases in the U.S. have dropped dramatically, from an average of 700,000 to 800,000 a week to 30,000 to 50,000 a week. About 66% of the U.S. population is now fully vaccinated against COVID-19, and deaths from the disease have declined steadily since January. We are clearly not in the same vulnerable place we were in 2020. The vaccines have provided some barrier to the virus, and that counts for a lot. But that immunity still isn’t enough to declare COVID-19 over.

Nevertheless, those numbers encouraged a push to loosen public health restrictions that have been in place since 2021—federal mandates that people wear masks in indoor settings, and on public transportation including subways, buses, trains and planes, as well as requiring proof of vaccination for certain gatherings at sports and entertainment complexes. In April, a U.S. District judge in Florida struck down the federal mask mandate, declaring that it was unlawful and that the U.S. Centers for Disease Control and Prevention (CDC) had overstepped its authority in imposing it. The Biden Administration is appealing the ruling, but in the meantime, airlines and most public transit systems no longer require passengers to wear masks.

That coincided with an uptick in cases of COVID-19—there’s no direct way to prove one caused the other, but the coincidence is hard to ignore. After remaining at about 24,000 to 25,000 new infections a week in early April, cases started to inch upward again at the end of the month to nearly 50,000 a week on average. Hospitalizations are also creeping upward, although those trends lag behind case rates.

Steps towards a truly endemic COVID-19 virus

Those trends suggest that it may be too early to relax our vigilance over COVID-19, which remains a potent threat for a number of reasons. First, no vaccine is 100% effective in protecting against infection or disease, and the COVID-19 shots are no exception. While highly effective in warding off the worst COVID-19 symptoms from the original virus strain emerging from China, the shots are less effective in protecting against newer variants of SARS-CoV-2. And the virus continues to mutate, with each version appearing to improve on the last strain’s ability to infect quickly and efficiently. Fortunately these changes haven’t led to a more virulent strain so far, but they could veer in that direction, and cause more serious disease on top of being more transmissible. If that happens, the vaccines and drug treatments currently available might provide little, if any, protection at all.

That leads to the second reason that COVID-19 isn’t fading into the background any time soon. Despite the effectiveness of the vaccines, scientists still don’t know exactly what it takes to fully protect someone from COVID-19. That question actually breaks down into two related queries: What does it take to prevent infection in the first place, and what level of immunity is needed to protect against serious illness? Even into the third year of the COVID-19 pandemic, scientists still don’t have solid answers for either.

Read more: Many Americans Are Celebrating the End of COVID-19. Here’s What It Feels Like When You’re Not

While the mRNA shots in particular are effective at curbing COVID-19 disease, reducing the rates of COVID-19 symptoms by more than 90% among people who were immunized, the vaccines have been less effective in protecting people from getting infected in the first place. That’s not unusual for a vaccine, since the best way to block infection is with a pre-existing store of antibodies that can stick to the virus and interrupt them from infecting cells—and before getting immunized, most people in the world didn’t have any antibodies against SARS-CoV-2. And even after getting vaccinated, antibody levels drop after a few months, which is why health officials have recommended booster doses. Those boosters have been slightly better at reducing risk of infection for this reason, but the vaccines are still not designed as a powerful way to stop infection.

They are far better at preventing serious COVID-19 disease. But even there, it’s still not clear exactly how much of an immune response, or what type, is enough to stop severe COVID-19 symptoms that can lead to hospitalization and even death. Studies of people who have been vaccinated, as well those involving people who have been naturally infected with SARS-CoV-2, are trying to shed some light on this, but scientists still can’t point to exactly what kind of immune reaction will be essential to finally push SARS-CoV-2 back.

Such knowledge about what scientists call the correlates of immunity could go a long way toward shaping U.S. policy on booster shots in the fall. For now, the U.S. Food and Drug Administration (FDA) and other public health experts are relying on antibody level data as a proxy to gauge how well vaccines work and what type of immunity is needed. But in a recent meeting of the FDA’s vaccine advisory committee, the experts raised concerns about how reliable the current metrics of antibody levels are in serving as surrogates for these correlates of immunity. Until further research reveals how much immune protection is enough, it’s not likely that the world will move past seeing COVID-19 as a continuing pandemic threat, albeit, as Fauci proposed, one that is under better control now than when it first emerged in 2020.

That’s why the White House, with the support of the CDC, is pushing back on lifting the federal mandate for mask-wearing on public transit, and stressing that while the hospitalization and death numbers are trending in the right direction, the virus is far from gone and is still a threat to public health.

It’s not likely that there will be consensus any time soon on when the pandemic shifts from even Fauci’s so-called “controlled” phase into becoming endemic. In the meantime, rather than waiting on broad declarations on whether the pandemic is over, some health experts are urging people to start making their own informed decisions about which behaviors and situations feel safe to them. If they have underlying chronic conditions that can put them at higher risk of severe COVID-19, such as diabetes or asthma, for example, or if they have compromised immune systems, it makes sense for them to continue wearing masks even on planes and trains where they aren’t required. Or if people live in households with elderly people or with children under six years old who aren’t eligible to get vaccinated yet, then continuing to wear masks in certain indoor settings and avoiding crowded situations might be wise.

Government and global health organization statements about the pandemic are critical for helping nations to navigate responses and allocate resources for addressing public health, but once those tools are in place, it’s up to us as individuals to use them in the combination and frequency that provides us with the most protection in our specific circumstances. Even if SARS-CoV-2 becomes endemic like the flu, it will remain a threat for certain groups, just as influenza does. For those people, it will be important to maintain all the behaviors that protect them from infection. For those who are less vulnerable, easing some of those protection measures might make more sense. While mandates have served as guides for the best way to battle the pandemic, going forward it will likely fall increasingly on individuals to rely on those guides to forge their own path forward as each of us learns to live with COVID-19, in whatever form it takes.

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