To understand what is a “pandemic”, we have to talk about what an outbreak, an epidemic and a pandemic mean, as well as the different levels of disease in a community.
When a certain disease is present at a relatively constant rate in a population within a certain geographical area, and remains at this rate, it is known as an endemic disease.
This endemic disease may continue to occur at this rate indefinitely.
For example, if we are used to having certain numbers of dengue cases or flu cases every year in Malaysia, that is our endemic rate.
When a disease occurs infrequently and irregularly, we call it sporadic.
When there are persistent high levels of a disease occurring, it is called hyperendemic.
An outbreak occurs when there is an increase, often suddenly, of the number of cases of that disease, above the usual expected number of cases in a particular area.
It is very much like an epidemic, except that an outbreak is the term used for a more limited area, and epidemic is used for larger, more widespread populations.
Epidemics are usually confined to one city or region, or even a country.
A cluster is an aggregation of cases that are grouped in a place and time, which is greater than the expected number of cases.
A pandemic is an epidemic that has spread over several countries and continents, and affects a large group of people.
For example, the Covid-19 outbreak was declared a pandemic by the World Health Organization (WHO) on Mac 11 (2020).
Pandemics happen when a bacteria or a new virus becomes capable of spreading rapidly and widely.
The word “pandemic” comes from a Greek word “pandemos”, which means “pertaining to all people” (“pan” means all and “demos” means people).
The cases and deaths in a pandemic are usually higher than an epidemic.
In our modern world, it is easier for pandemics to happen because of modern rapid travel by air and sea.
The pandemics we hear of nowadays seem to be caused by a novel (new) virus or subtype that has jumped from animals to humans.
But bacteria are just as capable of causing a pandemic, and increasing antibiotic resistance worldwide only contributes to that eventuality.
Sometimes, pandemics are caused by a virus or bacteria that mutates to gain a new ability to spread widely.
We humans have no immunity against a new virus, or an old virus or bacteria that has suddenly acquired the ability to spread rapidly.
That is why we succumb more easily to these infections.
The common flu occurs so frequently everywhere in the world and every year, killing so many people, that it is no longer considered a pandemic. It has become endemic instead.
We may still occasionally get seasonal outbreaks of the flu or an epidemic.
These are usually caused by a particular subtype of the flu virus that rises to prominence during that time.
In contrast, pandemics are usually caused by novel viruses.
These are some well-known pandemics in the the past:
The peak of this pandemic occurred from 2005 to 2012. The death toll at that time was 36 million people.
The earliest verified case of HIV infection was identified in a preserved blood sample from 1959 of a man from Kinshasa in the Democratic Republic of Congo, although the original spread of HIV is theorised to have started a few decades before that from the same city.
The virus has been with us ever since. There are currently 35 million people living with HIV.
Humanity has found a way to contain it with antiviral drugs, but it still exists.
- The 1968 flu
The death toll of this pandemic was one million people, with half a million in Hong Kong alone.
Called the Hong Kong flu, it first occurred in Hong Kong in 1968, and rapidly spread to Singapore and Vietnam, then the rest of the world.
- The 1956-58 Asian flu
This flu originated in China, and went all over the world.
Two million people died during this pandemic.
- The 1918 flu
The death toll for this flu was between 20 to 50 million people.
It killed primarily healthy adults, in contrast to the normal flu that usually kills the elderly, the weak and children.
- The sixth cholera pandemic (1899-1923)
Originating in India before spreading worldwide, the death toll in India alone was over 800,000 people.