Scientists look to the past to see the future – fr

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Scientists look to the past to see the future – fr


WWe are approaching the one-and-a-half-year mark of the world’s collective experience with the SARS-CoV-2 virus and the Covid-19 pandemic it triggered. At this point, it’s fair to assume that people all over the world are asking the same two questions: How will this end? And when?
There may have been a fleeting chance that humans were able to stop the spread of SARS-2 and bring it back to the wild, as happened with its cousin, SARS-1. But that door was firmly closed a long time ago. It also appears that another option – to vaccinate our way out of the pandemic – is an expensive toll highway that few countries will be able to access in the short term.

It probably sounds bleak, but don’t despair. The truth is, pandemics always end. And to date, vaccines have never played a significant role in ending it. (That’s not to say vaccines aren’t playing a critical role this time around. Far fewer people will die from Covid-19 from them.)

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But there were no flu shots in 1918, when the world was still unaware that the great flu was caused by a virus, H1N1. In 1957, when the H2N2 pandemic swept the world, the flu vaccine was primarily a tool of the military. During the 1968 pandemic, which brought us H3N2, the United States produced nearly 22 million doses of vaccine, but by the time it was ready the worst of the pandemic was over and demand declined. This “too little and too late” phenomenon reoccurred in 2009, when the world finally had the capacity to manufacture hundreds of millions of doses of H1N1 vaccine; some countries canceled a large part of their orders because they ultimately did not need them.

How did these pandemics end? The viruses did not go away; a descendant of the Spanish flu virus, modern H1N1, circulates to this day, as does H3N2. Humans have not developed collective immunity against them either. It is a phenomenon whereby a pathogen stops spreading because so many people are protected against it, because they have already been infected or vaccinated.

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Instead, the viruses that caused these pandemics have undergone a transition. Or more precisely, we did it. Our immune system has learned enough about them to fend off the most deadly manifestations of the infection, at least most of the time. Humans and viruses have reached immunological relaxation. Instead of causing devastating disease tsunamis, over time viruses have triggered small outbreaks of milder disease. The pandemic flu has become the seasonal flu.

Viruses have become endemic.

If the pattern continues, and SARS-2 is expected to join a handful of human coronaviruses that cause colds at some point, mainly in the winter when conditions favor their transmission.

When will this happen? This is the big unanswered question. “I thought we would have come out of this acute phase already,” admitted Maria Van Kerkhove, the World Health Organization’s leading coronavirus expert. Van Kerkhove’s thinking, however, is influenced by his categorical view that the world could stop the pandemic if countries only take the steps countries like New Zealand, Vietnam and others have taken. and control transmission.

“There is nothing – there is nothing – including variants of the virus, which suggests we may not have come out of the acute phase already,” she told STAT in a recent interview. . “Because it’s controllable.”

Experience from the last four pandemics – the ones mentioned above – would suggest that viruses evolve from pandemic pathogens to endemic sources of disease within a year and a half or two of their emergence. But all of these pandemics were influenza pandemics. A different pathogen could mean we’ll see a different pattern.

There may well have been previous coronavirus pandemics; There is a school of thought that a pandemic in 1889, known in medical history as the “Russian flu”, could in fact have been caused by one of the human coronaviruses, OC43. It is assumed that the four human coronaviruses jumped to people of an animal species; It is believed that OC43 originated in cattle, probably in the late 1800s. But this is in the realm of theory, not a conclusive fact, having taken place before the era of modern virology.

There is no historical record of the extent of illness and severity of illness caused by these other coronaviruses when they first started infecting humans or how long it took them to settle in. an endemic condition. As such, influenza pandemics are the closest thing to roadmaps. “In recent history it’s all been flu and the timing has been in a few years,” said Jennie Lavine, a biology researcher at Emory University who was the first author of a modeling article published in Science. who envisioned how the pandemic might end.

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