The definitions of pandemic, epidemic and endemic - and why it matters

The government is relying on Covid-19 jabs to shift the status of the disease in the UK from pandemic to endemic, the vaccines minister has said.

The “massive vaccination programme” will facilitate the change in status, Nadhim Zahawi told Sky News today. Booster jabs will provide further protection for vulnerable individuals in the coming months, with any future lockdowns “an absolutely last resort”. The latest update to the national rollout could see children aged 12 to 15 offered a first dose of the Pfizer-BioNTech vaccine as soon as 22 September, he told BBC Breakfast today.

More than 4.6 million people have died from coronavirus across the world since 2020 and more than 225 million cases have been reported, according to John Hopkins University data. With 5.7 billion vaccination doses now administered worldwide, what would a shift from a pandemic to an endemic look like?

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Classifying a pandemic, epidemic or endemic

The US Centers for Disease Control and Prevention (CDC) defines an epidemic as “an increase, often sudden, in the number of cases of a disease above what is normally expected in that population in that area”. A pandemic, on the other hand, “refers to an epidemic that has spread over several countries or continents, usually affecting a large number of people”.

For example, swine flu, or H1N1, was declared a pandemic by the World Health Organization (WHO) in 2009.

Endemic, by contrast, refers to the “observed level” of a disease within a population, CDC explains.The term refers to “the constant presence and/or usual prevalence of a disease or infectious agent” within a geographically bound population. Malaria is an example of an endemic disease.

Brian Labus, assistant professor of epidemiology and biostatistics at the University of Nevada, Las Vegas, notes that the term pandemic does not describe a disease’s severity.

“Because of their wide geographic distribution, pandemics usually affect a large number of people,” he wrote in an article on The Conversation last year. “While we usually think of pandemics in relation to serious, life-threatening diseases, even outbreaks of mild diseases could cross borders and become pandemics.”

WHO’s website explains that for a pandemic to be declared, at least one other country in a different region to the original source nation - in this case, China - must have a “community level outbreak”, and “human-to-human spread of the virus” must have occurred in at least two countries in one region.

Significance of terminology

Even when an outbreak is declared a pandemic, “the terminology doesn’t change anything about the severity of the disease or how we are responding”, said Labus on The Conversation.

And the risk to individuals will not change because of the terminology. “Even if an outbreak is spreading worldwide, how it is spreading locally and how people respond is what determines your risk,” he continued.

Ghebreyesus said WHO had been cautious in declaring a pandemic because the word, “if misused, can cause unreasonable fear, or unjustified acceptance that the fight is over”.

Ending the pandemic

An end to the pandemic may be in sight for the UK, but that won’t mean an end to coronavirus. "It's looking unlikely that we'll ever get to a point around the globe that we have enough immunity that covid goes away for good," Professor Lauren Ancel Meyers told the BBC.

And as populations adjust to “a new world in which covid is endemic”, there remain “challenges ahead”, noted The Telegraph commentator Andrew Lilico. Vaccine efficacy is one, he said, and restrictions around international travel are another. “But, in England at least, the coronavirus epidemic is now de facto at an end.”

SARS-CoV-2 “is likely to remain a more serious threat” than other types of coronavirus which already circulate among populations, The Atlantic reported. “No bright line” separates the virus from pandemic to endemic status; rather, some populations will “straddle the two” states throughout winter.

In the future, society will need to control the “continual threat” of the coronavirus by “adapting our work and leisure activities to turn an omnipresent virus into a manageable risk”, the American magazine said. Vaccination plays an essential role here.

For countries such as New Zealand, “the shift from a zero-Covid-19 goal to an endemic, low-burden goal may be challenging”, noted McKinsey & Company in August. And for at-risk countries, particularly those of lower and middle-income without access to enough vaccine doses to adequately immunise their populations, the time-frame for managing Covid-19 as endemic “is less clear”.