History

Epidemics have marked the history of mankind, modifying societies and influencing economic, political and cultural structures. They have been recounted regularly since Antiquity. 

T

he Athens plague, documented by Thucydides in 430 BC, killed up to a third of the Athenian population. The Antonine plague, suspected in reality to be smallpox, ravaged the Roman Empire between 165 and 180 AD, causing some five million deaths. Later, the Middle Ages were marked by major pandemics such as the Justinian plague, which began in 541-542 AD and was caused by Yersinia pestis. This pathogen was also responsible for the Black Death, between 1347 and 1351, which killed between 25 and 50 million people in Europe.

In modern times, epidemics have taken on a new dimension. Diseases introduced to the Americas by colonizers, notably smallpox, decimated up to 90% of indigenous populations in the 16th century. In the 19th century, cholera (caused by the bacterium Vibrio cholerae) struck repeatedly, wreaking havoc in Asia and Europe, particularly in densely populated urban areas.

The 20th century saw even more global pandemics. The Spanish flu of 1918-1919, caused by an H1N1 strain of the influenza virus, infected around a third of the world's population and caused between 50 and 100 million deaths. In the 1950s, poliomyelitis was one of the most feared epidemics. Fortunately, it was largely contained thanks to the vaccine developed by Jonas Salk in 1955. The emergence of AIDS, first identified in the 1980s, marked a new era in the spread of epidemics among the human population. Caused by the HIV virus (Human Immunodeficiency Virus), AIDS has led to major societal upheavals and caused some 40 million deaths to date.

Since the appearance of AIDS, epidemics have succeeded one another at an ever-increasing rate, highlighting the unfortunately persistent vulnerability of human populations to infectious agents, despite advances in medicine and biomedical technologies. The Ebola virus, first identified in 1976, has experienced several major outbreaks, notably in West Africa between 2014 and 2016, with over 11,000 deaths. SARS (Severe Acute Respiratory Syndrome), caused by a coronavirus (SARS-CoV-1), affected around 8,000 people and caused almost 800 deaths between 2002 and 2003. More recently, the 2009 H1N1 flu, nicknamed "swine flu", infected between 700 million and 1.4 billion people and caused around 284,000 deaths. Influenza pandemics have been complemented by other contemporary health crises, such as MERS-CoV (Middle-East Respiratory Syndrome - Coronavirus), which appeared in 2012, with a high mortality rate of 34%. Zika virus disease, emerging between 2015 and 2016, has been associated with severe birth defects. However, it was the COVID-19 pandemic, caused by SARS-CoV-2, that turned the world upside down between 2020 and 2023, resulting in over seven million deaths according to the WHO and permanently transforming human societies.

Several factors have contributed to this outbreak of modern epidemics. Rapid urbanization, by increasing population density in cities, has facilitated disease transmission. Globalization, with international travel, has enabled pathogens to spread rapidly. Deforestation, by increasing contact between humans and natural reservoirs of disease, climate change, which extends the transmission zones for mosquito-borne diseases (and other vectors) such as malaria, dengue fever and Lyme disease, increased agriculture and illegal trade in wild animals, are also major factors influencing the occurrence of epidemics.

Many of these factors result in increased contact between humans and wild animals or livestock. This explains why 75% of emerging and re-emerging diseases are in fact zoonoses, in which wildlife (e.g. yellow fever, SARS, COVID-19, echinococcosis) or farm animals (e.g. avian and swine influenza and bovine spongiform encephalopathy) act as reservoirs or amplifiers of disease-causing agents. Zoonoses are estimated to be responsible for 2.5 billion cases of human illness every year.

If we restrict our discussion here to human epidemics/pandemics, it is nevertheless important to draw attention to the major impact that animal epidemics/pandemics have on mankind. Indeed, as mentioned above, most human epidemics/pandemics are actually zoonoses which, in addition to being transmitted to humans, can compromise animal production and food safety. For example, the avian flu (H5N1) currently raging around the world is responsible for a massive slaughter of poultry and a sharp rise in the price of eggs, which has tripled in the United States.

More than ever, epidemics in the broad sense of the term are a major threat to humanity, despite scientific and medical advances. The WHO is therefore asking countries to prepare for what is commonly known as Disease X, a potential pandemic of exceptional severity, whose infectious agent is as yet unknown. This disease, added by the WHO (World Health Organization) to its list of priority diseases in 2018, could induce unprecedented mortality in the human population.

Unprepared States

The COVID-19 pandemic revealed the unpreparedness of governments in the face of epidemic and pandemic threats. The fight against epidemics and pandemics rests on several pillars:

1. fundamental research in the fields of infectiology and immunology ;
2. worldwide monitoring of the emergence and spread of infectious agents;
3. the ability to rapidly implement measures aimed at slowing down the spread of disease (e.g. containment and reducing the movement of people);
4. the ability to diagnose infectious diseases and identify healthy or sick carriers (screening);
5. the development of effective vaccines and the implementation of vaccination on a large scale;
6. the development of pharmacological treatments for infectious diseases and the sparing use of these treatments to avoid the development of resistance;
7. the ability to receive and treat all seriously ill people in hospital.

When the SARS-CoV-2 virus began to spread rapidly outside China, states reacted in different ways, depending on their level of preparedness and previous experience with pandemics. Some Asian countries such as Taiwan, South Korea and Singapore, having already faced epidemics such as SARS in 2003, quickly put in place rigorous screening, contact tracing and quarantine measures. In contrast, many ill-prepared European and American countries were slow to react, facilitating the rapid spread of the virus.

Containment has emerged as a key measure for slowing the spread of the virus, particularly in the absence of effective vaccines and treatments. However, its application varied in terms of duration, intensity and geographical coverage. China has instituted strict confinement in Wuhan and other regions, combined with technological surveillance measures. In contrast, Western countries, faced with social challenges, applied less stringent measures, with mixed results.

The pandemic also highlighted the limitations of healthcare systems in many countries. Faced with the massive influx of patients, governments stepped up efforts to increase hospital capacity, notably by building temporary hospitals, reallocating resources and training additional staff. Despite these efforts, critical shortages of intensive care beds, personal protective equipment (PPE; e.g. surgical and FFP2 masks and latex gloves) and respirators were observed, particularly in hard-hit regions such as Italy and New York.

Shortages affected not only hospitals, but also laboratories responsible for diagnosing the disease. Although diagnostic techniques were available, the reagents and plastics needed for screening were no longer available on the world market. For many years, the production of these consumables had been in the hands of a few multinationals, mainly based in China, who were unable to meet the massive demand from governments. States therefore had to resign themselves either to testing less than necessary, or to hastily relocating the production of reagents and plastics.

One of the most notable successes in managing the pandemic was the rapid development of effective vaccines. Thanks to coordinated efforts between governments, pharmaceutical companies and research institutions, several messenger RNA vaccines, such as those from Pfizer-BioNTech and Moderna, were brought to market in less than a year. This scientific feat, backed by substantial funding, has enabled vaccination campaigns to get underway rapidly. However, it is questionable why these efforts were not implemented with the same force after the SARS and MERS episodes, which were also caused by coronaviruses. Had this been the case, messenger RNA vaccines would have been developed even before COVID-19 appeared.

The COVID-19 pandemic underlined the need to improve the responsiveness of governments to future epidemics and pandemics. It also gave us the opportunity to identify all the actions needed to achieve this. For example, investing in basic research into epidemics in the broadest sense of the term and in more effective public health bodies, devising scenarios for responses to pandemics (depending on their nature) and ensuring that they can be rapidly implemented where necessary, strengthening epidemiological surveillance and screening systems, relocating the production of equipment and consumables needed to combat epidemics and acquiring sufficient strategic stocks, setting up better training for healthcare professionals in the field of epidemics and strengthening hospital capacities. These actions will enable us to better anticipate and respond to future health crises, while reducing their impact on society, the economy and healthcare systems.