A disease that will probably never be eradicated and others to come

Three years ago, Covid-19 disrupted the planet. The pandemic is not over, and scientists warn that other epidemics are to be expected, and they are learning from the crisis it has created to better prepare for them. “We are not yet” at the end of the epidemic, the World Health Organization (WHO) warned in early December.

While at least 90% of the world’s population has some form of immunity, “shortcomings in surveillance, testing, sequencing and vaccination continue to create the perfect conditions for the emergence of a worrying new variant that could cause significant mortality,” its director-general warned . Tedros Adhanom Ghebreyesus.

From pandemic to endemic virus

It is the WHO that declares the end of a pandemic. “It is always an extremely important moment, often the subject of controversy,” noted microbiologist Philippe Sansonetti during a symposium Wednesday at the Institut Pasteur, assessing that the organization was probably not ready to “whistle the end” of the pandemic.

What experts expect is a gradual transformation of the pandemic into an endemic virus that continues to circulate and cause regular resurgences of the disease. This is the case today with measles or seasonal influenza.

Covid and its “bad cases”

The SARS (severe acute respiratory syndrome) epidemic, which broke out worldwide in 2003 and claimed nearly 800 lives, was contained by isolation and quarantine measures. One virus, smallpox, was already declared “eradicated” in 1980 thanks to a WHO vaccination campaign. But this scenario remains extremely rare.

“In order to eradicate a virus, it is necessary that the disease is clinically visible, that there is no animal reservoir, and that you have a very effective vaccine that protects for life. Covid-19 ticks all the wrong boxes,” said Philippe Sansonetti. Some of the carriers of Covid-19 are actually asymptomatic, which affects isolation measures. And unlike smallpox, the virus is transmitted to animals and can continue to circulate among them and reinfect humans. Finally, vaccines provide good protection against severe forms of the disease, but little against reinfections, and booster doses are still needed.

Humans promote the transmission of viruses

For Etienne Simon-Lorière, director of the Evolutionary Genomics Unit for RNA Viruses at the Institut Pasteur, “today we let the virus circulate far too much”: every time it infects a person, mutations can occur and are likely to cause it to develop to more or less severe forms. “Although we would all like to think so, we have no reason to believe that he will become more likable,” he warned.

In addition, other respiratory viruses may emerge: since the emergence of Sras, Mers and Sars-Cov2, “a good dozen coronaviruses have been found in bats, which can potentially infect [l’humain] ”, noted Arnaud Fontanet, specialist in emerging diseases at the Institut Pasteur. About 60%/70% of new diseases are of zoonotic origin, that is, they are naturally transmitted from vertebrates to humans and vice versa. By occupying larger and larger areas of the globe, by traveling, by intensifying their interactions with animals, humans contribute to disrupting the ecosystem and promoting the transmission of viruses.

Anticipate rather than react

For Arnaud Fontanet, “much can and must be done at the start of an epidemic” to prepare for it. Denmark therefore decided in 2020 to be locked up very early, which made it possible to get out of it faster, he argued. Another necessity: “to have the capacity to develop very early tests”, at the start of an epidemic, to isolate patients very quickly. “Unfortunately, today we are still in the reaction, not the expectation”, laments the researcher.

At the international level, the “one health” concept that emerged in the early 2000s, which promotes a global approach to health issues with close links between human health, animal health and the environment, is new emphasis. A draft global agreement on dealing with pandemics was also under discussion last week in Geneva in the hope of avoiding the mistakes that marked the fight against Covid-19.

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