aWe have heard a lot since the start of the epidemic that viruses have a natural tendency to co-evolve with their hosts to become milder. The idea behind this theory roughly speaks for itself that if a particularly destructive virus kills its host quickly or is bedridden and reduces its social connections too much, it will not spread well. Thus the genes that make them highly pathogen will be gradually eliminated, and more benign strains will dominate. Which is why, in January, I met some virologists before magazine new world They said they expect COVID-19 to eventually take the same evolutionary path as the “four human coronaviruses”, which have spread among us for centuries and that hardly cause more than a cold.
Except … this trend continues in the long term – several years, even decades – and it does not prevent the emergence of more aggressive variables in the short term. Then it comes to a “general rule” with many known exceptions, to the point that some researchers are skeptical that the rule actually exists.
“A review of viruses that infect mammals and their hosts shows that there is not necessarily a link between virulence and co-evolution. The report says that viral infections that have been identified for too long in a species can be asymptomatic as can be fatal. Manuel Viral pathogenesis. The text gives an example of smallpox that came before its eradication in two types: variola major, which killed about 30% of those infected with it, and variola minis, which was fatal in only 1% of cases. However, the two strains have been preserved for centuries despite their enormous difference in virulence, a sign that switching to benign is not the only “strategy” that can work with the virus.
In the case of COVID-19, it appears that carriers become contagious before symptoms appear and infection peaks where symptoms have just started, according to an article. Posted in March in Science. Thus, the virus has nothing to lose when it becomes more virulent if the bulk of its transmission occurs before the disease becomes dangerous. But hey, he doesn’t have much to gain either …
It is not entirely clear
So what feature does it take? In the case of the ‘English variant’ (B117), which I will focus on here because it is the most common in Quebec, it appears to have clearly proven more contagious – between 40 and 90% more. According to estimates Posted in Science It goes without saying that if it gets better, it will eventually drive more people to the hospital. But then, for every 1,000 people who contracted it, does it cause more complications and deaths? Overall, it definitely looks like it, although it isn’t quite clear yet.
Infectious disease specialist who specializes in emerging viruses and the respiratory system, Dr. Jay Poivin told me not long ago that he was not entirely convinced that B117 was really more virulent, “but I changed my mind. […] Indicating that this alternative is more lethal and / or leads to more hospitalization, ”he told me last week in an email exchange.
M Mars, 2 studies – 1 published In the British Medical Journal And the other at nature He looked at this question, basically, the same way, too To some extent By matching “historical” B117 and COVID cases that occurred around the same time, in the same areas and in people of the same ages, then researched to see if there was a difference in the death rate after 28 days. Both concluded that the English variant was indeed more lethal, at around 60-65%. Note that another study in “prior publication” (which has not yet been subject to peer review, so should be taken into consideration with caution) also found, in March, that B117 in Denmark led to 64% increase in hospitalization, All the proportions preserved.
However, this work did not convince the entire scientific community, and some have criticized it for using a method that was not always reliable for determining the English variant or for the fact that they did not. It is not controlled by the influence of joint diseases.
In the past week, two additional studies appeared on the same topic in the medical journal The scalpel, And both concluded that, on the contrary, the B117 is no more ferocious than the historical strains (see Here And the Here). They also have their limits and they have them Not everyone is convinced, Mind you. For example, only one of them considered hospitalized patients with the English variant or “historic” COVID; However, the B117 could drive more people to the hospital, but once inside the hospital it wouldn’t make any difference – which means it’s more virulent but the design of this study would have prevented her from seeing it. for him. The other article was about volunteers who self-reported their symptoms and also have blind spots, including the fact that very patients generally do not participate (or much less frequently) in this type of study, and this may have caused a significant portion of it to be lost. It is a dangerous situation.
In short, the thesis that the English alternative is more fierce is not entirely unanimous. Now, if I trust the expert interviews I have given or read, as well as the large number of virologists I’ve seen chatting on my social media, the idea still remains. I don’t know if this is enough to speak of a “scientific consensus”, but it seems to me that the logical thing to do is right, until proven otherwise.