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. A new pandemic could begin anywhere where there is close interaction of people and either domesticated or wild animals. 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. Influenza. 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. Coronavirus. 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.
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.
Only by maintaining a healthy environment and animal populations can we hope to protect and ensure the security of human health. 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.
How do we prepare for the next pandemic?
The success of any preparations for the next pandemic relies on the strength of countries’ systems for detecting and responding to outbreaks. But at the same time countries must better cooperate to ensure more equitable distribution of the tools needed for preparedness and response. COVID-19 saw wealthy nations prioritize their own populations over a more equitable global response, arguably prolonging and extending the effects of the pandemic in the process. Some developing nations struggled to access the diagnostics, vaccines, and treatments they needed to respond effectively. The ACT-A (Access to COVID Tools Accelerator) was set up by WHO and partner organizations early in the COVID-19 pandemic. The intention was to more equitably distribute COVID diagnostics, treatments, and vaccines and to help countries use them efficiently. COVAX, part of the ACT-A, was created to ensure that all nations could access vaccines at a favourable cost regardless of their wealth. The world is better prepared for the next large outbreak or pandemic because of technologies developed for vaccines, diagnostic tests, and therapeutics. These technologies have built on years of investment in research and the COVID-19 pandemic has massively accelerated their development. If there is another influenza or coronavirus pandemic, the same technologies could hopefully be used to swiftly develop effective vaccines, diagnostics and therapeutics.
The world is also hopefully better prepared through improved regional solidarity, evident by African nations which, throughout the COVID-19 pandemic via the African Union, developed their own programme to purchase vaccines and therapeutics. A series of vaccine and diagnostics research and production facilities are now being set up across Africa, a scale of cooperation that had not occurred before. This collaboration may provide a route for stronger future pandemic-response planning in African countries. The greatest challenges to preparedness for the next pandemic may well be political. As in the current pandemic, national sovereignty must be respected but the challenge is to ensure such concerns do not override the solidarity required for an adequate global response.