There seems to be a decent amount of confusion around the difference between an epidemic, endemic, and pandemic. Let’s talk about that today, so we help understand the differences and where we are with COVID-19.
I’m Dr. Jeff Kingsley and welcome to another edition of Riding in Cars with Researchers. Let’s start with epidemic. We’ve seen epidemics of many different things before. We’ve seen epidemics of Zika, we’ve seen epidemics of viral illnesses in Africa, we’ve seen epidemics of bird flus, and other SARS that didn’t really reach the pandemic level. Epidemic. Demos came from the Greek democracy, the people, right? So an epidemic is something that right now is acutely infecting a region of people. Epi – think epicenter, right – a small region of people is an epidemic. A pandemic means all. The Panthéon was about the ability of all the people to get together in a singular location. So when something involves a much, much larger number of people, a larger geography, then we begin to call it a pandemic. There are no actual clear rules of when you say something is epidemic or pandemic. It’s a little bit of a judgment call. There’s some subjectivity there in where you go from one or the other.
Now let’s tackle endemic. Epidemic and pandemic were both about acute and the difference was the quantity. So, an acute something infecting a population in a small geography is epidemic and acute something affecting a large number of people or large geography is a pandemic. Endemic is where you lose the acute. So something is endemic, regardless of geography, when it is no longer acute. It doesn’t go away; it’s there over a long period of time. Influenza is a great example of something that is endemic. Influenza comes and goes. We have bad seasons, we have light seasons. It travels around the entire planet. Flu season in the northern hemisphere is the exact opposite on the calendar from flu season in the southern hemisphere, and it just continues to travel around the world. Sometimes with the flu (influenza which is endemic), we get such a bad version of the virus that acutely, it becomes really worrisome, and acutely we will once again call it an influenza pandemic. So acute is epi or pan and chronic is endemic.
So where are we with COVID-19?
COVID-19 started at the tail end of 2019, and then the world became very aware of it in early 2020. COVID-19 was an epidemic. It was an acute illness affecting a small number of people, a small geography. And then it rapidly spread to the world because today we’re a globe. We are not individual countries, we are not individual continents with ships and airplanes, traveling all over the place every single day. Nothing ever stays in a limited geography these days. COVID-19 very rapidly became pandemic and affected the entire globe. Now we’re in 2022 and we’re reaching that point where would we still call COVID-19 acute? Here’s why you would and why you wouldn’t. We’re still seeing waves of COVID-19 and I gave the example of influenza where influenza is endemic, but if you have an acute wave that is very dangerous, an acute wave that is capable of hospitalizing, infecting, potentially killing large numbers of people, then we’ll call that an influenza pandemic. These waves are the reason why we are still considering COVID-19 to be pandemic.
There is quite a bit of hybrid immunity right now. There’s quite a bit of immunity from prior infection, and there’s quite a bit certainly in the developed world of immunity due to a vaccine. And what we’re seeing is that the best immunity is hybrid immunity, which is the combination of having received a vaccine, plus having gotten the infection. It creates a much more robust type of immunity because immunity is actually very complicated. It’s not really a singular thing. It’s lots of cellular things that happen at the same time. Hybrid immunity is the strongest. In the developed world, we have quite a bit of hybrid immunity right now, which means that without a mutation, another big wave would be highly unlikely. With another mutation all bets are off. It could be that hybrid immunity is not enough to confer adequate immunity to prevent hospitalizations and deaths.
I think we are on the cusp of being able to call COVID-19 endemic. In fact, I’m encouraging calling it endemic today. I don’t think it still rates as pandemic in the developed world. Is it still pandemic in the developing world? Maybe because there’s not as much hybrid immunity. The developing world has quite a bit of immunity from prior infection, but very low vaccination rates, which means that the immune response is not as great as having been vaccinated, let alone vaccinated plus having had COVID-19 on top of that. But I certainly think that in the developed world, we should begin calling this endemic.
Could it again become pandemic or epidemic? Absolutely it could and that’s the world we’re living in and that’s fine. That’s what we’ve lived with influenza forever. It is endemic and periodically it becomes pandemic. COVID-19 should be treated the same way. I’m in favor of calling it endemic today.