After the Alpha and Delta waves, the arrival of Omicron was characterized by an increase in the number of infected people without saturating the resuscitation services of hospitals. This variant of the virus, more contagious but less virulent, offers hope that the next waves of SARS-CoV-2, the virus responsible for Covid-19, will be less and less virulent. But can Covid-19 really become a mild illness? Science and the future make a point.
The difference between virulence and transmissibility
“A distinction must be made between virulence and transmissibility. The virulence of a virus corresponds to the amount of damage it causes when it infects someone and the severity of the symptoms. This is called pathogenicity. This is very different from the transmissibility of the virus.“, recalls Dr. Petr Markov, an epidemiologist at the Joint Research Center of the European Commission, as well as the European Center for Disease Control. Modulating these two parameters for a new virus strain is a lottery, since the factors involved are numerous. At the heart of these mechanisms is selection pressure, which forces virus to develop. To understand how this process works, Petr Markov takes the example of an antelope and a cheetah.”When a cheetah tries to eat an antelope, it must run fast to save its skin. Antelopes that are too slow end up being devoured by cheetahs. Then there are fast antelopes that breed among themselves and which will give birth to antelopes faster than the previous ones. That’s how a trait develops in a population, and the same thing happens with viruses..”
A less dangerous virus so as not to kill its carrier?
The Covid-19 virus, in order to survive, must not spread quickly, but be transmitted to as many carriers as possible. Variants with mutations that allow the virus to be more infectious will tend to crowd out others like Omicron. Regarding its virulence, and therefore the severity of the symptoms it causes, SARS-CoV-2 is the subject of much speculation. “Several opposing evolutionary theories. Some say the virus can’t get too serious or it will kill its host and be unable to survive. In reality, the moment of infection is always much earlier than when the patient dies from Covid.“explains Dr. Jeffrey Shaman, professor at the Columbia University School of Public Health in the US.