The Omicron variant would reproduce more than the Delta in the upper respiratory tract, but less in the depths of the lungs, according to several studies. This could explain that it is more transmissible but less serious. However, researchers urge caution.
“The replication of Omicron is 70 times greater than that of Delta in the trachea but, 10 times less in the lungs”, explains Michael Chan, a virologist at the University of Hong Kong, who has worked on cell broths human.
At least three animal studies have come to similar results. None have yet been published in a peer-reviewed journal, but rather on scientific pre-publication sites.
The greater reproduction of the Omicron variant in the nose and throat could increase the amount of virus present in aerosols and droplets exhaled by infected people, and facilitate its implantation in a new person.
The hypothesis made headlines New York Times 1is January, from star journalist Carl Zimmer. But Michael Diamond, of Washington University in Saint-Louis, who compiled in his study the results of half a dozen laboratories having observed the phenomenon in mice and hamsters, was more circumspect this week than in his interview. with the New York Times.
“I’d rather have more human cell studies, like the one in Hong Kong, before concluding that’s what’s happening with Omicron,” says Dr.r Diamond in interview with The Press. “It is clear that Omicron is more transmissible, but it is possible that its lower severity is due to vaccination and not to less replication in the lungs. Ideally, one should check what happens with Omicron in naïve patients, who have never been infected or vaccinated. »
A first study of its kind, from South Africa, was prepublished on Friday on MedRxiv. It estimates a 25% reduction in the risk of serious hospitalization or death posed by Omicron compared to Delta in the unvaccinated. “It’s a fairly small reduction, observes the Dr Diamond. And we don’t know if these are patients who have already had COVID-19. »
D’s cautionr Diamond is understandable, according to Guy Boivin, infectious disease specialist at the CHU de Québec. “But I’ve seen the studies, and indeed there seems to be more replication in the upper airways and less in the lungs. »
Jonathan Lévesque, a pulmonologist at Maisonneuve-Rosemont Hospital, notes that patients with the Omicron variant seem to have less damage to the depths of the lungs, where gas exchange with the blood takes place, compared to other SARS variants. -CoV-2, the coronavirus responsible for COVID-19. “We see more of an impairment of general condition and bronchospasms,” says Dr.r Levesque. These bronchospasms affect the larger bronchi, at the beginning of the lungs.
This has led to changes in practice, says Dr.r Levesque.
An anti-inflammatory inhaler, Pulmicor, appears to be effective in reducing symptoms of the Omicron variant.
The Dr Lévesque, pulmonologist at Maisonneuve-Rosemont Hospital
According to him, the Pulmicor could be prescribed by a family doctor, even by telemedicine, to avoid a visit to the hospital by a patient having bronchospasms, sometimes called “blinks”.
The Dr Boivin, from the CHU de Québec, also publishes this week in the magazine Emerging Infectious Diseases a study on the interaction between different respiratory viruses.
“A British study observed that patients who had the flu before the first wave of COVID-19 in 2020 had a lower risk of infection and death, says the Dr Bovine. Rhinoviruses, which cause colds, also reduce the risk of COVID-19. In addition, last summer we saw a large number of cases of respiratory syncytial virus, whereas, normally, the peak of RSV occurs around the holidays. So there does seem to be interference between the viruses. »
The infectiologist from Quebec notes that patients with the flu and COVID-19 simultaneously often have more severe illness, but he does not think that means that COVID-19 increases the severity of the flu. “It’s just the combined effect of two diseases,” he says.
The next step, he says, is to see if SARS-CoV-2 interferes with other respiratory viruses and makes them less severe. Immunologists have argued on the contrary that confinement, by reducing exposure to cold and flu viruses, will undermine the immune defenses of the population and make these infections more serious.
“I think that the containment explains part of the low flu activity, for example, but that it does not explain everything, says the Dr Bovine. I think it is quite possible that there is interference from SARS-CoV-2. »