For many of us, the year 2020 might be the first time we were introduced to these epidemiological terms, such as “pandemic”, “epidemic”, and even “endemic”, as COVID-19 began to spread its devastating effect around the world. You may vaguely understand that these terms refer to infectious illnesses but what do they really mean and what differentiate these terms?
Pandemic, epidemic, or endemic?
“Pandemics”, “epidemics”, and “endemic diseases” are defined by the World Health Organization (WHO) based on the rate of disease spread. What makes an epidemic and a pandemic different is not the severity of the disease, but the scale of its spread. Hence, a pandemic is not necessarily worse than an epidemic or an endemic disease. Pandemics do have the largest potential to cause worldwide disruption, but this depends on the specific disease and how we manage it collectively.
Here are the definitions of these terms:
Endemic: An endemic disease is consistently present in a specific region or population with a fairly stable prevalence. This makes the spread of the disease predictable. Examples are:
- Malaria is endemic to some parts of Africa due to the higher temperature
- Dengue fever is endemic to tropical and subtropical regions like Malaysia
- Hepatitis B is endemic worldwide, with higher endemicity in Africa and Asia
Epidemic: An epidemic is a sudden and rapid increase in the number of disease cases above what is normally expected in a specific region or population. It can happen when a new disease appears in the population or when an endemic disease becomes more prevalent. An epidemic disease is not necessarily contagious and may refer to other diseases or health issues with a prevalence higher than the projected occurrence in a population. Examples are:
- Zika virus epidemic in Brazil (2015-2016)
- Ebola virus epidemic in West Africa (2014-2016)
- Opioid epidemic in the US due to the increasing use of opioids and overdose cases in the past decades
Pandemic: A pandemic happens when a disease spreads across multiple countries or continents, impacting a large number of people. A disease may be declared as a pandemic if it spreads at a very fast rate, with more new cases reported every day. An ongoing epidemic may turn into a pandemic if it spreads beyond the originating region or population. Properties of the pathogen, population immunity, or severity of the disease do not play a role in determining whether a disease is a pandemic. Examples are:
- COVID-19 pandemic caused by SARS-CoV-2 (2020-2022)
- Swine flu pandemic caused by H1N1 influenza virus (2009)
- Great Influenza pandemic (also known as Spanish flu) caused by H1N1 influenza virus (1918-1920)
Other key terms
Other terms may be used to describe the spread of disease in a population:
- Sporadic: When a disease happens rarely or occasionally. This includes tetanus that tends to happen only in unvaccinated individuals or foodborne illnesses such Salmonella or coli infections.
- Hyperendemic: When there is a persistent presence of a disease at a higher level in a population compared to other populations. For example, in parts of Africa, as many as one in five adults has HIV, hence the disease is considered hyperendemic in those places.
- Cluster: When a disease occurs at a higher rate in a population, while the exact cause or the actual number of cases may be uncertain. For example, the cluster of cancer cases that arises after a chemical contamination event or a nuclear plant accident.
- Outbreak: Has the same meaning as an epidemic but is typically used to describe a disease spread that is more limited geographically.
Has COVID-19 become endemic?
This is a question that has been asked many times since the world started reopening after the COVID-19 pandemic. To answer this, we need to understand what it means for COVID-19 to be endemic. When COVID-19 has reached the endemic phase, it will continue to be present at a certain predictable level or trend in the population. The closest example is influenza, which is typically present at an expected level throughout the year in Malaysia.
Yet, being endemic is not necessarily a good thing since the disease can still have severe effects on patients. Plus, it is possible for an endemic disease to turn into a pandemic again. COVID-19 is no longer categorised as a pandemic and predicted to be endemic sooner or later. But experts are split when determining whether COVID-19 is already endemic since there is still a lot of unpredictability with SARS-CoV-2.
Regardless, continued surveillance and vigilance are necessary to prevent another pandemic from happening. Other than practising personal hygiene, taking COVID-19 booster doses is also part of preventive measures recommended to everyone, especially high-risk groups such as the elderly and people with underlying conditions or weakened immune systems. Whether it’s endemic, epidemic or pandemic, let’s continue to prioritise our health and safety!
By Dato’ Dr Musa Mohd Nordin, Consultant Paediatrician & Neonatologist, and
Dr Husna Musa, Paediatrician
