It’s been nearly a month and a half since California became the first state to officially adopt a policy for COVID-19 as an “endemic” disease. But even at the time, Gov. Gavin Newsom didn’t really explain how it was determined that Omicron was now endemic or even what that actually meant in practical terms, especially when Omicron BA.2 cases may be threatening another COVID bump, albeit less than those of Delta or Omicron BA.1.

Armchair epidemiologists have been saying on social media for months that COVID is or soon will be endemic, but many of them seem to think that means COVID has become less dangerous and that we stop efforts to control the spread of it.

Instead, as Kent State University epidemiologist Tara Smith told me, endemic simply means “something we’re stuck with.” That is, COVID will “remain with us for the foreseeable future, and we can (roughly) predict the number of cases and deaths it will cause in a year’s time.” But that doesn’t tell us what we should, or shouldn’t, do about it.

After all, flu has been endemic for over a century, and we still prepare for flu season every fall, starting with annual vaccination campaigns. HIV has been endemic for four decades, and scientists are still actively working on developing a vaccine because we haven’t given up and decided to just “live with it.”

“Relatively Predictable”

To make sense of what endemic actually means — and what it doesn’t mean — I reached out to Smith and a couple other real (non-armchair) epidemiologists, first asking for examples of endemic diseases in the U.S. people are familiar with. In addition to flu, whose cases fluctuate with mild or particularly deadly seasons, food-borne illnesses like E. coli or salmonella are endemic, Smith said, as are sexually transmitted infections like gonorrhea, HPV, syphilis, and chlamydia.

The most dangerous strains of HPV have declined since introduction of the HPV vaccine, but no vaccines exist for gonorrhea, syphilis, and chlamydia, however, and cases hit an all-time high for the sixth year in a row last year. Broadly speaking, then, endemic doesn’t necessarily mean a disease can’t be increasing to potentially alarming rates, even if the rise has been gradual and we’ve been living with it for a long time.

There’s not an exact threshold for determine when a disease reaches endemic status, Smith said. It’s usually just when a disease “becomes predictable,” which can involve “increases and drops, or ‘waves,’ of cases, but generally these become relatively predictable over time, such as the seasonality we see with influenza,” Smith said. Few would say right now that COVID has reached a point where we consider it predictable.

Matthew Fox, an epidemiologist at Boston University, agreed that there isn’t necessarily a fully accepted precise definition for ‘endemic.’

”Some use it to mean contained to a specific area, but I think the more common meaning that people are using with respect to COVID is controlled at an acceptable level typically at a somewhat steady state (it can be seasonal but predictable),” he said. But, he adds, “We have to define what we consider to be an acceptable level.” And therein lies the rub.

“Some think even very low levels are not acceptable if it is leading to deaths,” Fox said, while others seem to think endemic means “low enough that I can not have it involved my daily life” — hence when we can end restrictions. But it’s not that simple. “The challenge is that we are likely to see rises and falls in cases for some time and we may want to take precautions when cases are rising and relax them when they are waning,” he said, echoing Smith’s point that “we don’t know yet if it will settle into a predictable periodicity like we see with influenza.”

Historical Perspective

Monica Green, a medical historian previously at Arizona State University, said the meaning of endemic often fluctuates in her field, with researchers defining it for the particular time and place they’re studying, but it still generally means “a disease is commonly circulating in a given population or region.” She pointed out that non-infectious diseases can be endemic too, such as diabetes, and she diseases no longer endemic in the U.S. are still be endemic and serious outside the U.S., like tuberculosis and malaria. But like Smith, she said determining when a disease crosses over into “endemicity” is trickier to answer. With endemic basically meaning the “status quo,” it hasn’t typically had a time element to it, she said.

“This is why discussions the past few weeks between historians and public health people have been so interesting, because the new usage presumes that you can watch a disease moving from introduction to a new population to epidemic surges to ‘endemicity,’” she said. “This is a very new concept.”

In fact, she said, there’s no historical precedent to watching in real time as a new disease enters the human population, circulates and leads to varying states of immunity from infection and vaccination, and gradually becomes endemic. “We’ve never had a new disease and its vaccine come online in such quick succession before,” she said. HIV, for example, doesn’t yet have a cure or a vaccine, and Ebola didn’t really become endemic even after a vaccine was developed.

Endemic Doesn’t Mean Harmless

When I reached out to Dominique Heinke, a postdoctoral researcher and epidemiologist, she pointed me to the Nature article “COVID-19: endemic doesn’t mean harmless,” in which author Aris Katzourakis, a professor who studies viral evolution at the University of Oxford, described “endemic” in his first sentence as “one of the most misused [words] of the pandemic.” Again, he explained that endemic simply means disease rates are neither rising nor falling. Sure, the common cold is endemic and more a nuisance than a life-threatening illness for most people, but malaria is endemic too and killed more than 627,000 people in 2020.

“A disease can be endemic and both widespread and deadly,” Katzourakis writes, but it’s not “an excuse to do little or nothing,” just as we don’t sit by and let diseases like hepatitis C, malaria, or flu circulate as though we’re helpless to do anything about them. “Stating that an infection will become endemic says nothing about how long it might take to reach stasis, what the case rates, morbidity levels or death rates will be or, crucially, how much of a population — and which sectors — will be susceptible,” he writes.

Heinke added that she agreed with colleagues, such as Green, Boston University epidemiologist Ellie Murray, and Johns Hopkins nursing and public health researcher Cecília Tomori, that calling a disease endemic “tells us nothing about severity or the need for protective measures nor is it an inevitable state of an infectious disease.” Green, Murray, and Tomori spoke with COVID Calls in early February about the meaning of endemic and ways it’s been misunderstood by the public. And one of the biggest of those misconceptions continues to be this idea that becoming endemic means we can just kick back and stop worrying about a disease.

”I think the assumption is that endemic means we no longer have to worry about it, or that endemic means mild. Neither is true,” said Smith, who also mentioned malaria as a leading killer of children. “Endemic means that we’ll constantly have to deal with this infection. Maybe it will become more mild and fade into the background. Maybe it won’t. We should be planning for multiple possible scenarios.”

And So… Now What?

In a way, the “true, precise” definition of endemic is almost irrelevant when people are using it in such different ways and for different agendas. If anything, the term has become a bit of a smokescreen to avoid dealing with the situation at hand, which is a disease that is still very much here and with us, even if rates are mercifully lower at the moment.

“I don’t think ‘endemic’ adds anything to the conversation,” Heinke said. “It’s mostly being used to downplay the continued severity of COVID and provide cover for removing mitigation measures.”

Fox implied a similar concern, that the lack of precision in the definition has meant that “people use it to mean whatever they want it to mean,” he said. “Some want it to mean contained. Some want it to mean low level of transmission. Some want it to mean a stable level.” It’s not that any of those are correct or incorrect. Rather, “I think we need to have a conversation about what metrics we will use to define easing restrictions.”

Smith agreed that “we need to have a real conversation about control, and how much resources we will be willing and able to dedicate to such.” Mask mandates are gone throughout most of the country now, and the Biden administration recently allowed people to order their next batch of free at-home COVID tests. But funding is running out for free COVID testing, treatment and even vaccines, leaving uninsured people in a lurch.

“What will we have in the near and farther future regarding public availability of case and hospitalization counts? Will vaccines be mandated for K-12 schools?” Smith asked. “All of these are aspects of ongoing disease control, but it is unclear if they will be funded or even available in every state as after the Omicron wave ends.”

And those are just questions in the U.S. Worldwide vaccination remains too low, and it’s unclear how much help wealthy countries like the U.S. are going to offer to countries with fewer resources. If there’s one thing the pandemic made clear, it’s that the disease threatens every country as long as it threatens any countries.

“Right now, I think no one knows what the plan is going forward,” Smith said. “We’ve spent so much time responding to each crisis that a long-term plan hasn’t been put forth.”

And while people continuing arguing over what endemic means and whether COVID is endemic or not, the questions that really matter go unanswered.