If it is far too early to envisage the end of the Covid-19 pandemic, the past examples shed interesting light on how this crisis can end.
You have probably already asked yourself this question, since the beginning of the Covid-19 pandemic. How and when will it end? “It is extremely difficult to grasp and predict, particularly in the case of a new epidemic, the characteristics of which are not well known”, warns Jean-Pierre Dedet, professor emeritus at the Faculty of Medicine of Montpellier and author of Epidemics, from the Black Death to the A / H1N1 flu (Dunod, 2010). If it is far too early to provide a definitive answer, a return to the epidemics that have marked the history of mankind will shed light on what awaits us.
Black plague, Spanish flu, smallpox, SARS, seas … Franceinfo explains what the end of the epidemic tunnel might look like.
An epidemic can go away naturally
The end of an epidemic closely depends on the particularities of the responsible microbe and its mode of transmission. The possible ends are divided into two large families: either the disease disappears naturally, or man finds a solution.
• Seasonality. It is she who makes the flu disappear, each spring in the northern hemisphere, in particular because his virus prefers cold and humidity.
• The mutation. As it spreads, the pathogen, be it a virus or bacteria, can develop into a less lethal, less dangerous, or easier to control form. Syphilis, for example. “In the first descriptions, this disease was presented as fearsome and deadly”, says Patrice Debré, immunologist and author of Life and death of epidemics (Odile Jacob, 2013). “Its gravity has lessened thereafter.”
The mutation can have the opposite effect. In the case of the plague, it is the passage of the bacillus from the stomach of the rat to its blood which allowed its transmission to the rat flea, then to humans. “The bacillus was able to produce a kind of plug which obliterates the downpour of the flea, says Patrice Debré. When the flea draws blood from its host, it is “regurgitated inside the human body and can contaminate it”.
• Environmental modifications. After terrorizing Europe, from the 14th to the 18th century, the plague was swept from our continent by the Norway rat. This brown rat ousted its cousin the black rat, the reservoir of the disease transmitted to humans via its fleas. “This rodent carried a bacillus close to the plague, which had immunized him against the disease. This is a very special case, in which the disease was stopped in the tank”, explains Jean-Pierre Dedet.
• Collective immunity. Finally, there is, for certain diseases, the biological response of our body: it is the famous collective immunity. Upon first contact with a disease, our immune system produces antibodies that can prevent reinfection. “We think it takes 60% of immunized people in a population to block. This is what happened for most flu, including the Spanish flu of 1918, and for measles”, explains Patrice Debré. Doctor and philosopher at the CNRS, Anne-Marie Moulin notes that the Greek historian Thucydides had already noted, in his account of the plague of Athens, in the 4th century BC, that “those who survived could take care of the sick and if the plague returned they would be protected”.
An epidemic can disappear after human intervention
When the spontaneous evolution of the disease or its environment is not enough, man can intervene.
• Isolation of patients to cut the chains of transmission. “This is what was done with Sras in 2003”, analyzes Jean-Pierre Dedet. In the early 2000s, this epidemic, already caused by a coronavirus, had been limited to a few outbreaks in southern China and Toronto. Assessment: 8,000 cases and 774 people killed.
• Improvement of hygienic conditions. It is in this way that cholera, transmitted by water, disappeared from certain regions of the world. “It was eradicated from Europe and America by the sanitation of the cities, the sewerage. It almost did us a service, because until the XIXth century, the cities were cesspools”, retraces Jean-Pierre Dedet.
• The vaccination. The vaccine helps to provoke collective immunity. The most emblematic case is that of smallpox, declared eradicated in 1980 after a massive vaccination campaign led by WHO.
• Treatments and vector control. Finally, the fight against the vector (for example, mosquito control campaigns to fight against malaria), the development of an effective treatment (which exists for plague) or a better knowledge of the mechanisms of transmission, can make it possible to control a disease. This is what happened with Argentine hemorrhagic fever. “There were local epidemics of this disease carried by a little mouse, the transmission of which was not understood. We realized that this coincided with the arrival of the combine harvesters”, says Patrice Debré. The rest is in his book: “Trapped by the infernal mechanics, the mice are caught by the claw reel, then minced, crushed and pulverized in the form of an aerosol of blood and urine, dispersed by the shaker and the straw crusher to take it out of the steel monster, where the farm workers stand “. Once this risk was identified, the use of masks by them helped to contain the disease.
An epidemic may not stop
Not all epidemics have to end. One can fail to find a vaccine, as in the case of AIDS. The pathogen can evolve and adapt to the techniques put in place to counter it. The disease can continue to circulate, either in the animal reservoir or in the environment. This is the case of the plague, which reoccurs episodically in its “inveterate homes”, like Madagascar. “You cannot get rid of the rat, especially in contexts of poverty, where it is a commensal of man “, point Anne-Marie Moulin. The doctor also recalls that the “Cholera returns from the moment when there are problems of access to drinking water, we saw it in Haiti, after the earthquake of 2010”.
Can the Covid-19 never disappear? The history of coronaviruses and humans offers us “the two extreme examples” Jean-Pierre Dedet points. “The SAR has been completely contained, but the Sea, which comes from the dromedary, has lasted for ten years”, explains the specialist. It is unclear in which category the Covid-19 will fall.
An epidemic can go on in our heads
An epidemic is also a social, economic, political and psychological phenomenon. If there is a link between the medical end and the social end, the calendars do not always coincide. Isabelle Séguy, historian at the National Institute for Demographic Studies (INED), studied the plague that struck Marseille and Provence at the start of the 18th century. From a medical point of view, the city was freed from the plague in July 1721. “The resumption of ordinary activities is very gradual, over several months, due to the caution of the authorities and the fear of people”, she notes. Weddings, to recompose decimated families, resumed at the first signs of the epidemic’s decline, in November and December 1720. Economic activity restarted more slowly: the city was deconsigned in November 1722, international trade only resumed in January 1723 and did not intensify until the summer. Fear strikes not only inside the city, but also outside. “In the past few months, this has more to do with distrust than anything that comes from Marseille”explains the historian.
Psychologist at the Graduate School of Public Health, Jocelyn Raude explains that this mental end is determined by two factors: the uncertainty around the disease and the “perceived controllability of risk”.
The more we have the feeling of being in control of a risk, the less it worries us.at franceinfo
“Typically, the highest health risks in our country, alcoholism and smoking, are very little anxiety-provoking, because they are considered to depend on individual will”, illustrates the psychologist.
The specialist, who participates in programs to observe our behavioral, emotional and cognitive reactions to Covid-19, hesitates between two scenarios already observed in Western societies.
First possibility: addiction to risk, which leads to an end to the epidemic in the mind, while the dynamics of the disease continue (as was the case for AIDS). Second hypothesis: the mirror effect, with “maintaining a high level of preventive behavior” and very lasting changes, as the epidemic is over in terms of health. “Some anthropologists claim that social codes in Asia may have been shaped by the experience of epidemics”, he explains. Populations “set up social norms that emerged in an epidemic situation, and maintained them afterwards, like not touching your hands”. These two hypotheses can also overlap in society. Response in the coming months.
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