What’s the difference between an epidemic and pandemic?

While some people use the terms 'epidemic’ and ‘pandemic’ interchangeably, these two terms have different meanings. An epidemic is a term that is used to describe a problem or disease that has grown out of control. Medically speaking an epidemic is defined as widespread occurrence of a disease in a particular community at a particular point in time. An epidemic occurs when the number of people experiencing an infection or disease is greater than the number expected within a country or part of a country.

It is when a disease spreads beyond a country's borders and becomes widespread across different countries at the same time - an epidemic becomes a pandemic. A pandemic is a disease outbreak of global proportions. 

The word pandemic comes from the Greek word pandemos which means "belonging to all people" (pan = all; demos = people).

What causes pandemics?

A pandemic is usually caused by a new virus strain or subtype that becomes easily transmittable between humans, or by bacteria that become resistant to treatment with antibiotics. 

Sometimes, pandemics are caused simply by a new ability for the disease to spread rapidly, this was the case with the Black Death in the 14th century.

Humans may have little or no immunity to a new virus. A new virus does not have to be able to spread from person to person, but if it changes or mutates, it can easily begin to spread. In this case, a pandemic may occur. In the case of the flu, seasonal outbreaks (or epidemics) are usually caused by subtypes of a virus that is already circulating among a population.

A pandemic tends to affect more people than an epidemic, and they can be more deadly. Pandemics can also lead to more social disruption, economic loss and overall hardship.

After a pandemic emerges and spreads, humans do begin to develop some immunity, but this takes time. The virus subtype can then circulate among humans for several years, leading to occasional epidemics (of influenza, for example).

Various agencies around the world, such as the World Health Organisation (WHO) and the Centres for Disease Control and Prevention (CDC), monitor the behaviour and movement of viruses, in a bid to keep outbreaks of disease under control. 

Some of the worst pandemics throughout history

  • Plague of Justinian 541 A.D.
  • Black Death: 1346-1350
  • Cholera 1899-1923
  • Spanish Flu (H1N1) 1918-1920
  • Asian Flu (H2N2) 1957-1958
  • Hong Kong Flu 1968-1969
  • Avian (H1N1) 2009

The Spanish flu pandemic, from 1918 to 1920, claimed 100 million lives. It is considered the worst pandemic in history.

Some viruses are present in animals, but rarely spread to humans - but sometimes this does happen. Health authorities are always concerned when a case of an animal virus is passed to humans, as this may be an indication that the virus is changing. 

In recent years, there has been increasing concern about viruses that have been linked to camels (Middle Eastern Respiratory Syndrome or MERS) and monkeys (Ebola).

If a pandemic were to emerge in our current times, there are many challenges to overcome because the world is much more internationally mobile than was the case in earlier centuries. More mobility increases the chances of a virus or disease spreading; faster communication networks increases the risk of panic and increases the possibility of people travelling in an attempt to escape a disease, which as a result can spread the disease further - if unsuspecting infected people are also travelling. A vaccine could take months or years to become available, because pandemic viruses are novel agents. 

Despite major medical advances in recent years, it is unlikely that the world would be able to obtain full protection against a potential pandemic.

Katie Burt

Katie Burt

When not found with a laptop at my fingertips, it's likely I'll be running, swimming, attempting to cycle or seeking out decent coffee.

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