COVID will likely shift from pandemic to endemic — but what does that mean?

Most people are wondering when and how the COVID pandemic will end and there are still no easy answers.

The word “endemic” is regularly mentioned, especially among public health leaders and experts as they discuss potential future scenarios. So, it’s important to define exactly it would mean for COVID to be endemic.

Scientists predict COVID will become endemic over time but there will still be sporadic outbreaks where it gets out of control. The transition from pandemic to endemic will likely play out differently in different locations around the world.

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‘Outbreak’, ‘Epidemic’, ‘Pandemic’ and ‘Endemic’

First let’s recap the public health terms Australians have been increasingly using in conversation over the last 18 months. These words cover the lifecycle of disease and include “outbreak”, “epidemic”, “pandemic” and “endemic”.

An outbreak is a rise in disease cases over what is normally expected in a small and specific location generally over a short period of time. Foodborne diseases caused by Salmonella contamination provide frequent examples of this.

Epidemics are essentially outbreaks without the tight geographical restrictions. The Ebola virus that spread within three West African countries from 2014–2016 was an epidemic.

A pandemic is an epidemic that spreads across many countries and many continents around the world. Examples include those caused by influenza A(H1N1) or “Spanish Flu” in 1918, HIV/AIDS, SARS-CoV-1 and Zika virus.

Finally, the normal circulation of a virus in a specified location over time describes an endemic virus. The word “endemic” comes from the Greek endēmos, which means “in population”. An endemic virus is relatively constant in a population with largely predictable patterns.

Viruses can circulate endemically in specific geographical regions, or globally. Ross River virus circulates endemically in Australia and the Pacific island countries, but is not found in other regions of the world. Meanwhile, rhinoviruses which cause the common cold circulate endemically around the world. And influenza is an endemic virus we monitor for its epidemic and pandemic potential.

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What’s the usual path from pandemic to endemic look like?

Over time and thanks to public health efforts from mask wearing to vaccination, the pandemic could disappear like small pox and polio did — or it might gradually become endemic.

Host, environment and virus factors combine to explain why some viruses are endemic while others are epidemic.

When we look at the SARS-CoV-2 virus that causes COVID, we see it is infecting human hosts with no prior immunity.

In terms of environment, the virus transmits better in cold, dry, crowded, close-contact, confined settings with poor ventilation.

Each virus has its own characteristics, from speed of virus replication to drug resistance. The new COVID strains are transmitted faster and cause different symptoms.

Viruses are more likely to become endemic if they become adapted to a local environment and/or have a continuous supply of susceptible hosts. For COVID these would be hosts with low or zero immunity.