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.
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.says Dr. Jeffrey Shaman, professor at the Columbia University School of Public Health in the US.Even if you count up to 6 million official deaths, or even three to four times as many, since all cases cannot be declared, these 20 million deaths are only a tiny fraction of the 7.7 billion people inhabiting the planet. This shows that Covid spreads widely before it kills, and that it doesn’t kill enough carriers to make selection pressure less strong.“So the virus has enough time to replicate in different people before the patient dies.”It’s the same principle for HIV, the AIDS virus. Patients who ignore each other may pass it on for several years before dying.“, adds Dr. Petr Markov.
There is no way to know what the next option will look like or whether existing vaccines will still be effective against this new strain. If the next option remains close enough to the previous ones, given that the population enjoys some immunity either through infection or vaccines, then serious forms should not increase dramatically. However, this immune defense must be clearly distinguished from a more harmless virus: protection resulting from a vaccine or infection does not mean that the virus has become less virulent. “At the moment, RNA vaccines still protect against serious or fatal forms of the disease, but are getting worse and worse at protecting against symptomatic forms. [et sans gravité] covid“, – says Dr. Markov. It is also unknown whether infection with Omicron will give good protection against more severe variants in the future.
The Only Solution: Immunity Evasion
The vaccine itself plays a role in the selection pressure that the next option will generate. Through its action, the vaccine creates an immune memory in the vaccinated population. This immunity, which slows down the spread of the virus, also puts it under immune pressure. “If a virus invades a population that is considered naive, that is, unvaccinated and uninfected, no immune system will be able to block it. The virus can travel and infect people without problems‘, says Dr. Peter Markov.
If its ability to replicate (known as “viral fitness”) increases, it becomes more contagious. This is exactly what happened with Alpha and Delta, two waves that spread before vaccines. The two variants considered can more easily pass from organism to organism. On the other hand, in a population where there is a form of immunity, the virus will run into closed doors. It is in this context that the selection pressure comes into play: only variants with a mutation that eludes antibodies will be able to thrive and suppress organisms that have become resistant. Then this new variant becomes the only one capable of infecting humans, there is no more competition. As this mechanism repeats itself wave after wave, we hypothesize that, over time, the next strains will not be more contagious in nature, but rather arise as a result of immune evasion.
Finally, the Omicron variant may be less virulent than the previous ones, but its high transmissibility mechanically leads to an increase in serious cases. In recent weeks, France and other countries around the world have seen a resurgence of the epidemic. Parallel to this rise in cases, many countries, including France, have decided to lift health restrictions such as wearing a mask indoors or skipping vaccinations. In France, the number of hospitalizations is almost no longer declining, with hospitals admitting a total of 20,742 patients against 20,919 patients as of March 15. At a press conference on Tuesday, March 22, the World Health Organization (WHO) found that several European countries, including Germany, France, Italy and the UK, had raised too much.brutallytheir response to COVID-19. Before the next, perhaps less dangerous option appears, it will first have to wait for the end of this fifth wave of Covid-19, which has been raging since November 2021.