The next pandemic
This article explains how a new pandemic might occur, what it could be, and what measures might prevent such an event. First, to explain the issue, it’s useful to understand some key terminology:
An epidemic is an outbreak of a disease in a particular location.
A pandemic is an outbreak of a disease which spreads to and occurs in many different geographic areas at the same time.
Endemic diseases are established and circulating regularly in populations. Some endemic diseases such as influenza can have surges in transmission or have epidemics at certain times.
A pathogen is an organism which causes a disease to its host, including but not limited to viruses.
When could the next pandemic happen?
It is impossible to predict when the next pandemic will occur as they are random events. They can begin anywhere in the world where animals and humans are in close proximity as pandemics most often originate when a pathogen transfers from an animal in which it lives to a human never before infected with that pathogen.
When emergence in humans occurs, one of three outcomes are the result: the pathogen causes an illness in a single person, as with rabies; it causes a wider outbreak, such as the Ebola virus disease in the Democratic Republic of Congo in 2018 and 2020; or it causes a pandemic with the potential to become endemic, such as HIV.
The large influenza pandemic in 1918 is a major historical point of reference but there have been several less lethal influenza pandemics since then. Some experts call HIV a pandemic which has become endemic.
Infectious disease outbreaks are most likely to occur when a series of risk factors happen together. An El Niño weather event in 1998 caused flooding in Kenya, Somalia, Sudan, and Tanzania which meant cattle and humans were forced to live closer together on the remaining dry land. This increased the risk of cross-species pathogen transmission. Due to a shortage of vaccines, the cattle were unvaccinated against the Rift Valley Fever virus, a common infection among ruminant animals in the region.
The flooding created more breeding sites for mosquitoes, leading to a rapid increase in the mosquito population. Mosquitoes are one means of transmission of the Rift Valley Fever virus from animals to humans, and from human to human. This facilitated emergence of the virus in human populations which was then transmitted from human to human.
Alignment of all these risk factors resulted in a major outbreak of Rift Valley Fever among the region’s human population.
Where could the next outbreaks occur?
Efforts have been made to predict where pandemics may originate by identifying sites of emergence in the past, such as mapping all known emerging-infection incidents from the 1940s to the early 2000s and predicting that emergence would occur at one of those sites. But emergence is a random event both in time and place and mapping has not been a reliable predictor.
Influenza pandemics historically emerged in southern China so that area was the focus of attention as a possible source of new strains of the influenza virus. But the 2009 H1N1 ‘swine flu’ pandemic is thought to have originated in Mexico and/or the southern US rather than in China.
Even if there was a genetic-sequencing library of all organisms carried by wild animals linked to the animals in which they are found, such a database would be difficult to keep updated. At best, it could give an idea of the origin of a newly identified pathogen but scientists cannot predict an outbreak using such databases. A new pandemic could begin anywhere where there is close interaction of people and either domesticated or wild animals.
What could be the next pandemic?
There are a few known pathogens – either viruses or bacteria – that can cause pandemic- or epidemic-prone diseases.
Most influenza viruses originate in wild waterfowl. The H1N1 swine flu virus had its origins in bird populations thought to have then transferred infection to pigs where it mutated in such a way that it could transmit easily from human to human – once humans had been infected directly by pigs.
Respiratory infections represent one of the highest risks of an epidemic or pandemic after emergence and human-to-human spread, as infected humans often create aerosols when they cough, sneeze, or speak loudly.
The influenza virus is an unstable virus which originates in wild waterfowl which transmit infection to domestic birds and poultry, and they then pass it on to animals and/or humans. Sometimes, the influenza virus mutates into a form which can spread easily in humans. In those circumstances a pandemic can occur.
Before the COVID-19 pandemic, advance plans in most countries anticipated a pandemic strain of influenza virus. But countries in Asia which had experienced outbreaks of SARS coronavirus in 2003 tended also to take coronaviruses into consideration.
There have been three outbreaks caused by coronaviruses in humans during the past 20 years. Each originated among wild animals and one of these viruses – SARS-CoV-2 – is the cause of the COVID-19 pandemic.
In addition, there are four coronavirus strains that are endemic in humans, causing the common cold. These are thought to have emerged from animals at some time in the past. SARS-CoV-2 will most likely become the fifth endemic strain.
Highly lethal infections with a short incubation period, such as the Ebola virus disease, are much less likely to become pandemic.
They cause severe illness early in infection that incapacitates and kills those infected, giving the virus little time to be transmitted to others.
By contrast, HIV has a long period when it does not cause signs and symptoms but can transmit from human to human, making it well-adapted to becoming endemic.
SARS-CoV-2 has a relatively low level of mortality compared to the Ebola virus. In the future it is possible, but not predictable, that a more lethal coronavirus strain could emerge.
What role does climate change play in the next pandemic?
The leading causes of climate change can also increase the risk of pandemics occurring. Deforestation, urbanization, and the enormous livestock husbandry required for a growing meat-production industry all bring more and more animals into closer contact with humans. This in turn increases the likelihood of pathogens ‘jumping’ from animal to human.
It is generally accepted there will be another pandemic and that, through many of the same activities that fuel climate change, humans are giving pandemics more opportunities to occur.
That is why a ‘one health’ approach is so important – the animal health, human health, and environmental sectors must work together to rapidly detect and respond to pandemic risks.
Pandemic prevention and preparedness must be considered in the context of the ecosystem and animal health as much as in that of human health.
Only by maintaining a healthy environment and animal populations can we hope to protect and ensure the security of human health.