Is coronavirus really losing strength?

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The patients hospitalized in the past weeks seem less serious than those of the early stages of the epidemic. Some experts claim that the virus is losing potency, a possible hypothesis, but still not supported by the available data

He has been hearing for a few weeks: the coronavirus may have started at lose strength. Several specialists engaged in the front row in the fight against Covid-19 have repeated it several times, to explain the fact that in hospitalized patients the symptoms very serious in the first weeks of the epidemic. In short, good news, except that scientific opinions are not univocal. With phase two just starting, and its inevitable trail of controversy and reprimands, the denials have now started to become more tranchant, and accomplices unhappy exits like that of the Governor of Veneto Luca Zaia, according to which a possible weakening of Covid would demonstrate the nature artificial of the coronavirus, the same idea that an epidemic virus can become less lethal begins to seem yet another hoax. The truth? There would be nothing strange if SARS-CoV-2 was evolving towards less dangerous forms, but the clues available at the moment are not sufficient to prove it.

The perception of clinicians on the other hand comes from experience in the ward. An important source of information on the disease, which however can mislead even the most scrupulous doctor: there are many possible explanations for the fewer serious patients observed at this stage of the epidemic, and the weakening of the virus is only one of these, perhaps one of the least likely. To confirm it, they will be needed in vitro studies is extensive case studies from the lanes, all information that takes time to be collected and analyzed properly. “Personally, I don’t think it is likely that Sars-Cov-2 is weakening”, Confides in Wired Maximum Andreoni, an infectious disease expert from the Tor Vergata University of Rome. “The sensation arises from a reduction in mortality and a lower number of hospitalizations in intensive care, but these are phenomena that can also be explained by themselves: the lockdown has decreased the sick, and therefore we see less of them with severe symptoms and we record less died in our hospitals“.

It’s not all: COVID-19 in fact, it is a disease that tends to mow down the most fragile people, and it is therefore possible (especially in the areas most affected by the epidemic) that the virus ended up to select the patients most at risk in phases initials (spreading for example in the Rsa), and after the many deaths (and fortunately also the many recovered) of the last few months it is now inevitably to hit less fragile people, thus causing symptoms and exist less inauspicious. Therapeutic abilities, although still incomplete, have also improved. Hand in hand with the conditions of the hospitals and the number of ICU places, creating less dramatic working conditions for doctors. So many pieces that could have contributed to improving the prognosis of patients.

The possible explanations, in short, are manifold, and at this stage it would be better to avoid externalizing what are simple sensations, and stick to scientific data“, go on Andreoni. “The virus may well have weakened, but to say it, in vitro studies must be carried out to verify the existence of less aggressive strains, genetic studies that identify mutations in the viral genome and their effects, and clinical studies that really certify a lower incidence of outcomes inauspicious or access to intensive care“.

The immunologist has a different opinion Guido Silvestri, of the Emory University Atlanta, which in its usual update on Covid does not hide a cautious optimism in this case. Calculations in hand, the professor believes that the reduction in lockdown-related infections only partially explains the decrease in severe cases and ICU admissions seen in the past few weeks. Even the lesser overload of hospitals and therapeutic improvements (still limited) would not properly explain the situation. For this reason, silvestri considers the possibility that the virus has started to lose power to be concrete: both for dynamics co-evolutionary already seen in the case of other diseases, both because the higher temperatures (as usually happens with coronaviruses) could have favored infections related to a minor viral inoculum, that is, contagions caused by a smaller number of viral particles, which normally cause diseases with less severe symptoms.

All hypothesisobviously needing irrefutable data to be confirmed. But that should not be branded – as done by someone in the past few days – like pseudoscience. That viruses can lose aggression over time is indeed known, and easy to explain (in retrospect of course) in one perspective evolutionary: the optimum for a virus is not to kill its host, but rather to be able to replicate is infect as many people as possible. Moving from one patient to another, the natural mutations of the virus are subjected to a selection process, which can lead to the spread of less aggressive strains, less capable of killing but precisely for this reason more effective in spreading among the population.

Similar examples of co-evolution between viruses and hosts have been documented in the past, for example in rabbits, where a virus with a very high lethality, greater than 90%, was studied, which spreading among the population and quickly came to lose aggressiveness. producing strains with less than 50% lethality”, Concludes Andreoni. “However, these are very complex processes, too much for predict the outcome of the evolution of a priori viruses. In other cases, such as that of chickenpox, viruses behave in the opposite way, becoming more aggressive passing from a first patient to a new infection. In the case of the new coronavirus we know that it is accumulating mutations in its genome, but to say what effects they will have on its phenotype it will still take months“.

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