“Endemic” Explainer

Infection and Spread Uncertainty and Misinformation

“We’re moving from pandemic to endemic.”

We’re hearing this phrase tossed around more and more. In certain anti-science twitter circles, the hashtag #endemic is used as shorthand for the opinion that COVID-19 is overhyped, we’ve all been duped by the media into a hysteria over the pandemic; the vaccine is unnecessary; and everything should return to normal immediately.

What is the difference between endemic and pandemic disease? Is there any truth to the idea of moving to endemic disease?

Let’s review terminology first.

Epidemic: a disease outbreak that is at higher than the baseline or usual levels for that disease. When a disease is brand-new, the baseline is always zero, so any amount of disease is going to be higher than the baseline. A pandemic is simply an epidemic that has affected the whole world.

The word endemic is an adjective. It describes a situation where a disease is *typical* in a certain area or environment. It is used in exactly the same way to describe the plants, animals, and microbiota that are native to a region. In public health, which usually concerns itself with the health of human beings, it’s used to describe a disease that is common in a certain human population.

Measles is endemic in parts of Africa. Polio is endemic in Afghanistan and Pakistan. Chicken Pox is endemic in the United States. These diseases occur at a sustained, continuous, predictable pace in those populations.

Endemic does not mean:

– The end of the pandemic. Endemic is not a play on words. It’s a scientific term coming from the Greek roots “en” (within) and “demos” (people).
– The end of everyone caring about the pandemic.
– Just a whole lot of disease all over the world (that’s a pandemic).
– That COVID-19 is no big deal.

An example: rabies is endemic in the state of Wisconsin. Do we simply live with the threat of rabies with no intervention or attempt to prevent outbreaks?

No. No we don’t. In fact, we go to tremendous lengths to prevent rabies. Even though there have been only four cases in Wisconsin since 1959, we worry about rabies–a lot. We vaccinate our animals annually. If you’re bitten by an animal (including a household pet who has never been outdoors) the animal has to undergo a 10-day observation for signs of disease. If rabies is suspected, the victim has to complete an expensive and difficult postexposure prophylactic treatment. By universally vaccinating companion animals, in most high-income settings we’ve reduced our exposure to rabies to the point where we don’t have to vaccinate all the humans. (Though if you are traveling to a high-rabies area, it might still be given as part of your travel vaccines.) For rabies, as for other diseases, endemic does not mean “this disease is no big deal.”

Someday, we probably will have areas of the world with endemic COVID-19. But that’s a long way off. To get there, we would need high vaccine coverage or natural immunity across every age group, worldwide. And that goal is years away.

When we do get there, we’ll likely have an ongoing vaccination campaign similar to what we already have for pertussis or measles. We may have ongoing, perhaps seasonal smaller outbreaks among the population that is too young to be vaccinated with occasional tragic outbreaks in higher risk settings such as nursing homes and prisons. Outbreaks may become annual, with some years worse than others but never producing a crisis.

There’s another epidemiology term that might be more like our near future: hyperendemic. Hyperendemic describes “persistent, high levels of disease occurrence” in a population. But not wave after wave of epidemic disease, which is what the world still faces today.

Endemic also does not mean exhaustion. I know–I’m truly, deeply exhausted too. We are all bone tired to the point of emotional paralysis. To the point of thinking any amount of risk is acceptable, if only it means no more pandemic-decisions. But that is not what “moving to endemic” means. That’s pandemic burnout, and it’s a different public health problem altogether.

More reading about pandemic, epidemic, and endemic:

Mailman School of Public Health


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