Coronavirus: What's the difference between an epidemic and a pandemic?

It's important to be cautious about how we talk about Covid-19 in order to avoid panic, says the World Health Organisation

Joanne Ma |

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Epidemic or pandemic? Wording matters when it comes to discussing the coronavirus.

As the coronavirus continues to dominate headlines and conversations around the world, many people are wondering how exactly we should define the outbreak: epidemic or pandemic?

Last week, the World Health Organisation (WHO) addressed the confusion.

“We appreciate that people are debating whether this is a pandemic or not,” WHO chief Tedros Adhanom Ghebreyesus told reporters on March 2. “I have said it before and I’ll say it again: WHO will not hesitate to describe this as a pandemic if that’s what the evidence suggests. But we need to see this in perspective. Of the 88,913 cases reported globally so far, 90 per cent are in China, mostly in one province.”

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In other words, the WHO does not yet believe we are facing a pandemic. But can we take this as good news? What is the difference between an epidemic and pandemic, and why does it matter which one we are tackling?

In fact, the way we define an outbreak has nothing to do with total number of infections, or how deadly they are in nature. It all depends on the distribution. 

Although the coronavirus has spread rapidly in recent months, with 29,550 cases outside China as of Monday, 77 per cent of those are confined to just four countries. Of the other 104 affected countries, 54 have reported 10 cases or fewer, and 19 have reported only one case. Some countries appear to have already contained the virus, with no new cases reported in the past two weeks, and more than 85 countries remain virus-free. This is why the WHO is still defining Covid-19 as an epidemic.

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The WHO defines an epidemic as the occurrence of an illness in a community or region that is in excess of normal expectancy.

The phrase “in excess of normal expectancy” is worth noting, says Professor Joseph Sriyal Malik Peiris, an expert in virology at the University of Hong Kong. 

He explains in an online course that even a single case of smallpox today would constitute an epidemic, because we wouldn’t normally expect to see any – the disease was declared officially wiped out in 1980. 

Even if Covid-19 does become a pandemic, the advice for staying safe will remain the same.
Photo: Shutterstock

While an epidemic refers to a sudden rise in infections in one or several communities, a pandemic describes something on a much larger scale – a disease that has spread throughout the world, reaching several countries or continents. It is likely to be a new disease that people are not yet immune to, and so is able to spread through populations quickly. However, it is not necessarily deadly. The words “epidemic” and “pandemic” do not describe the severity of a disease, only its geographic reach. The suffix “demos” means “people”, while “epi” means “among” and “pan” means “all”. So we can understand an epidemic as a disease that stays among a certain group of people, while a pandemic is one that affects all people. 

Yet despite the difference in meaning between these terms, there can still be confusion when it comes to categorising new outbreaks. 

Trisha Torrey, a US patient consultant, says in an article for the site VeryWell Health that even experts often blur the distinction between the two terms. For one thing, the nature of an outbreak can change very quickly. One moment, it might be under control; the next, it could become a global crisis. It’s difficult to regularly and accurately adjust the way we talk about it.

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Authorities also tend to be cautious about how they refer to diseases, according to the US Centres for Disease Control and Prevention (CDC), because certain terms can cause alarm. 

Take “dem” out of the word “pandemic” and you are left with “panic”, says Professor David Isaacs, a researcher in infectious diseases at the University of Sydney, in Australia. In his 2010 paper, he describes how the declaration of the 2009 swine flu as a pandemic created unnecessary fear, causing health services to be swamped and governments to overspend on antivirals and vaccines. Some countries also took extreme security measures. Australia, for example, upped its border checks to levels normally only used in the wake of a terrorist attack. 

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“The WHO pandemic plan was based on rapidity of spread more than on severity,” writes Isaacs. “The rapid escalation to the highest level of intervention seemed in retrospect to have been overcautious.”

Ultimately, our system for categorising diseases is an imperfect one. Isaacs suggests ditching the terms “epidemic” and “pandemic” altogether when talking about outbreaks, and instead only labelling diseases according to their actual threat to public health.

Even if the WHO does decide to upgrade Covid-19 to “pandemic” status, the advice for staying safe remains the same: wash your hands regularly, avoid crowded areas, and refrain from touching your eyes and mouth.