How Do Epidemics End? – 12th European Congress on Tropical Medicine and International Health, 28th September – 1st October 2021

By Maisie Jones, Key Correspondent and Professional Intern with the Irish Global Health Network

Date: 09th November 2021

This session took a different perspective on a health topic, and looked at epidemics from a historical standpoint. Historian Dr Erica Charters lead this session and took us on a journey through time to explore questions like what characterises the end of an epidemic, and who has the authority and expertise to declare an epidemic over? 

Dr Charters’ talk draws on preliminary research from a project that she is coordinating at Oxford University that examines this very large question of how epidemics end. The project involves over 40 researchers including epidemiologists, biologists, archaeologists, historians, and political scientists.  

Dr Charters begins by making the point that when we compare how much attention we spend on studying the origin and the unfolding of an epidemic, by contrast, we spend far less time studying the ending of epidemics.

Furthermore, when we do delve into the ending of epidemics, it becomes clear that the ending of an epidemic is not the same as the end of the disease, and there are multiple endings to an epidemic, not only across the world, but even within one society. Consequently, when we focus on endings, we can see that epidemics are not solely a biological phenomenon, but also a political, cultural, and social phenomenon. 

There have been several epidemics throughout history, and these are often presented in a linear manner, as if they all had a defined beginning and end, and occurred one after the other often with disease-free gaps in between. 

In reality, epidemics are less clear cut. While the beginning of epidemics are often distinct, using scientific metrics such as increased incidence, case numbers, transmission rate etc., the end of an epidemic is often more ambiguous; a more long, drawn out, and often contested process. 

In this talk, Dr Charters uses the example of the Ebola epidemic in West Africa, which was officially declared over in 2016, to demonstrate this. The World Health Organisation (WHO) actually declared this epidemic over several times.

They first declared that Liberia was Ebola free in May of 2015, the second declaration in September of 2015 more soberly reported “an end to Ebola transmission in Liberia”. Ebola was again identified two months later. And so in January of 2016, the WHO cautiously announced that the latest Ebola outbreak in Liberia was over adding that more flare ups are expected. It then declared the official end of West Africa’s “public health emergency of international concern” for Ebola on the 29th of March 2016. As its declaration clarified, this was not the end of the disease.

Instead, the WHO explained Ebola transmission in West Africa no longer constitutes an extraordinary event, that the risk of international spread is now low, and that countries currently have the capacity to respond rapidly to new virus emergencies.

We can see that with each of these declarations, the language changed, from a definitive end of disease, to a more ambiguous and cautious end of transmission and somewhat temporary end of the current outbreak. This points to the reality that in fact epidemics rarely conclude due to the end of the disease.

As we know, smallpox is the only human disease to have been eradicated, and although a few select epidemics such as SARS have been declared ended when cases among humans have ceased, this is not the case with most epidemics.

The 2009 H1N1, or Swine Flu, pandemic was declared by the WHO in August 2010, to be in a “post-pandemic period”. The WHO explained that in this post pandemic period, cases and outbreaks due to the H1N1 virus are expected to occur according to seasonal patterns of influenza.

In April 1712, Frederick IV of Denmark declared the end of a plague epidemic through a national day of prayer and thanksgiving, as well as the reopening of the city gates, even though cases of plague were still observed. In the week when Queen Victoria declared a national day of thanksgiving upon the great decrease of cholera in 1849, there were still 11 deaths from cholera recorded in London alone.

So rather than the end of disease, epidemics are more often marked by a perceived control of disease and a resumption of normal life and activities. As Dr Charters puts it, the end of an epidemic is when the drama ceases; when societies attention is no longer focused on the crisis of disease but shifts to reflecting on the social, political, and economic repercussions of the epidemic.  

Another point Dr Charters considers is that often epidemics end at different times in different places. She uses two examples to demonstrate this point.

The first is the HIV and AIDS epidemic, which she says may have ended for most in the Global North, but in some ways, it simply moved and continued on as an epidemic for many in the Global South. 

The second example she uses is plague and how the second plague pandemic, which ran between approximately 1350 and 1830, receded from Europe, while most of the world did not witness anything like an end. She says it’s more accurate to suggest that plague simply went dormant in a few select countries for a short period of time, while remaining active within rodent populations where it remains endemic today, and with scattered human cases regularly reported throughout the world.  

Furthermore, rather than this linear pattern of epidemics, with one ending and another beginning, there is often more of an overlap. Many epidemics happen simultaneously, with more than one disease present, cases fluctuating in waves, one disease peaking while another troughs, or indeed more than one peaking at a time.

Look at the example of Kenya, Dr Charteris says, where the current Covid-19 pandemic is ongoing alongside concurrent outbreaks of Ebola, Cholera, TB and others, these diseases constantly interacting with each other and with society.  

Dr Charters believes that this image of a history of a long line of epidemics, all with a beginning, a middle, and an end, is an attractive one. It gives us the illusion that we have conquered disease and therefore can do so again, that we can end this epidemic like we have ended all others. Epidemiology formed itself on this optimistic belief in human ability to control disease. However the control of disease is not only on humans but on ecology and climate. 

So back to the original question; when do epidemics end? The simple answer according to Dr Charters is that they don’t. They do not disappear formally or abruptly, they simply fade out, slip under the radar, become someone else’s problem.

But, she says, by focusing on ends, or non ends as the case may be, we can pay attention to the full context of individual outbreaks. It allows us to question the very category of an epidemic. We understand disease differently at the end stage, so if in the outbreak stage, we could channel that end stage understanding of disease, it might help us re-frame, and rethink our long-term approach to managing disease.