'Endemic' Doesn't Mean What You Think It Does

Health officials have been warning for months that Covid-19 isn’t going away; instead, it’s much more likely to become endemic. Many also believe the highly contagious Omicron variant, which has continued to drive up case counts around the world, could get us there.

While moving from our current pandemic to an endemic state certainly sounds like a move in the right direction, health experts also caution that it doesn’t necessarily mean what people think it does. It’s certainly not the “normal” reality people lived up until 2019. Nor is our path to endemicity clear cut.

So what does ‘endemic’ actually mean?

As the US Centers for Disease Control and Prevention explains, endemic “refers to the constant presence and/or usual prevalence of a disease or infectious agent in a population within a geographic area.”

The endemic level of disease in a given area is basically the baseline of that disease in a particular place. But it’s not necessarily the desired level of disease, the CDC clarifies. A disease could be considered endemic but still be pretty widespread.

“An endemic disease is an infection that always remains in a given population,” Vincent Hsu, executive director of infection control at AdventHealth, tells HuffPost US. “It might be limited to a particular geographic area, such as malaria, but could also be a widespread infection that has seasonal patterns, such as influenza, or continues throughout the year causing generally mild illness, such as the common cold.”

And knowing when exactly the transition from pandemic to endemic has happened is difficult, because health officials and epidemiologists may have different thresholds for when we’ve hit a sufficiently predictable, non-disruptive point of living with Covid. It’s a pretty nuanced term.

“Practically speaking, for Covid to become endemic, we would need to be at a point where Covid is sufficiently commonplace that it is not causing severe disease resulting in hospitalisations and death,” says Jay Lee, a family physician in Costa Mesa, California. “In other words, we need community immunity against Covid to be high enough that we are not seeing the levels of hospitalisation and death we continue to see now.”

Endemic and mild disease are NOT necessarily the same thing.

Moving from our current state (a pandemic) to endemic disease sounds like a good thing, and in many ways it is. But some experts worry that the general public is assuming that endemic disease is automatically less damaging or dangerous.

We could get to a point where Covid is considered endemic, but its impact on many people who are infected is not minimal. (Again, think of malaria, which is endemic in parts of the world and can be deadly.)

There could also still be unpredictable disruptions caused by the virus that would prompt restrictions and closures that would not feel at all “mild” at a society level. If the virus continues to infect relatively large numbers of people, it has more opportunities to change its genome.

Take flu as an example. Most people who get the illness recover within a few weeks, but for some, it is deadly. Also, we sometimes get flu pandemics which, as the CDC explains, occur when a new virus emerges that is able to spread from person to person in an efficient and sustained way.

“What we see with influenza is decades between major pandemics, and the major pandemics are due to shuffling of segments of the flu virus genome, which are known as genetic shifts,” infectious diseases expert Stuart Ray, vice chair of medicine for data integrity with Johns Hopkins Medicine, tells HuffPost.

Those shifts are what cause the major flu pandemics we’ve experienced, like H1N1 in 2009. But it’s not yet clear how much time we might get between genetic shifts with Covid. And if the virus is still infecting large numbers of people, it has more opportunities to change its genome.

“A part of me is hopeful that with this Omicron wave, we’ll generate enough immunity that we don’t see a lot of harm from future infections, and that we will reach a mild endemic state,” Ray said. “But I don’t know how stable that will be. And we might be dancing on a knife’s edge.”

... But we can have a controlled Covid endemic under the right circumstances.

That said, all of the experts who spoke to HuffPost for this story expressed cautious optimism that we can get to a point where Covid is endemic and we’re not caught off-guard by constant new disruptions or dangerous new variants.

“We may reach an endemic state where we have a relative equilibrium of a fairly high rate of infection which fluctuates ... but the fluctuations are narrow enough that people would say this is endemic. We’re not having a big pandemic. Or even epidemics, but just sort of a smouldering rate,” Ray says.

Whether Omicron will get us there isn’t clear yet.

Anthony Fauci, the nation’s top infectious disease expert, has said it’s not clear whether Covid will become endemic in 2022 as a result of Omicron. “I would hope that that’s the case. But that would only be the case if we don’t get another variant that eludes the immune response of the prior variant,” Fauci said.

Experts like Lee express tempered hope, noting that we’ll likely know more about endemicity as we emerge from the Omicron surge in the coming months.

“Think of this surge as the 10th round of a heavyweight boxing match, and we are enduring a flurry of punches like we haven’t seen yet,” he says. If we hit sufficient community immunity, we’ll be able to have a knockout. If not, we’ll have to endure some more rounds.

There are still a lot of unknowns that could impact when we hit the levels of widespread immunity necessary for Covid to become endemic.

One is simply how long immunity lasts for people infected with Omicron. Another is about what kind of variants could arise as the virus continues to spread and evolve. SARS-CoV-2 is not very stable genetically, and new variants could be more transmissible or more likely to cause severe disease — or both. Just because Omicron has generally been milder than what proceeded it does not necessarily mean that would be the case with future variants.

What we do right now can influence the timeline and potential severity.

People’s behaviour as we potentially near the transition from pandemic to endemic disease will make a difference in how and when we get there, experts say. Vaccination, improved ventilation, masking, social distance in times and areas of high transmission – all of those efforts continue to be critically important.

If getting close to an endemic state “causes people to relax the use of benign mitigation efforts, like wearing masks when they’re indoors in crowded places at times when transmission rates are high, then we’re going to take longer to get to that mild endemic state,” Ray warns.

“Exactly how Covid-19 plays out from here is anyone’s guess,” Hsu says. “At this point, vaccinations and boosters continue to be the single most effective way to prevent severe illness and spread to others.”