Evidence is increasing that the new Omicron variant of the coronavirus causes milder symptoms of COVID-19 compared to previous strains. However, panic still dominates the world, fearing a return to the early days of the coronavirus that saw thousands of deaths daily. According to official figures, over 5.4 million people have died since the virus first appeared in China in December 2019. The United Kingdom, the United States, and even Australia, which had been largely immune to the pandemic for a time, are now recording record levels of new infections.
In new studies conducted on mice and hamsters, researchers found that Omicron causes less damage to the lungs compared to previous strains, as its impact is limited to the upper respiratory tract: nose, throat, and trachea, according to The New York Times. While the animals tested generally experienced milder symptoms, scientists were particularly surprised by the results seen in Syrian hamsters, a species known for suffering severe illness from all previous virus strains. Dr. Michael Diamond, a virologist at the University of Washington and a co-author of the study, stated, "This was surprising; all other strains severely affected these hamsters."
Diamond and his colleagues discovered that the level of Omicron in the noses of hamsters was similar to that in animals previously infected with the coronavirus. However, the levels of Omicron in the lungs were one-tenth or less than those of other variants. These new animal studies aim to assess the severity of the Omicron variant, particularly as scientists can conduct tests on animals living in conditions similar to humans. Previous variants, especially Delta, caused substantial damage to the lungs and severe breathing difficulties that could sometimes lead to death.
COVID-19 infections begin in the nose or mouth and spread to the throat; mild infections do not extend beyond that. However, when the coronavirus reaches the lungs, it can cause severe damage. Immune cells in the lungs can overreact to the virus, killing not only infected cells but also uninfected ones. This can cause rapid inflammation, leading to scarring of the delicate lung walls. Furthermore, damaged lungs could allow viruses to escape into the bloodstream, leading to clots and damage to other organs.
Many lung cells carry a protein on their surface called "TMPRSS2," which can inadvertently assist viruses in entering the cell. However, virologist Ravindra Gupta from the University of Cambridge found with his team that this protein does not bind well with Omicron. As a result, Omicron does not infect lung cells as Delta does, despite having larger genetic mutations that help it cling to human cells. In contrast, cells in the upper airway tend to not carry the TMPRSS2 protein, which explains the evidence of Omicron being present more in the nose and trachea than in the lungs.
Dr. Gupta remarked, "You cannot predict the behavior of the virus from mutations alone." Concurrently, a team from the University of Glasgow independently reached the same conclusion. However, Dr. Diamond noted that he is waiting for further studies on humans rather than animals before accepting the hypothesis that the TMPRSS2 protein is the cause of Omicron's milder symptoms.
While increasing studies confirm that the severity of Omicron is lower than previous strains of the coronavirus, scientists are still investigating its transmissibility. Sarah Cherry, a virologist at the Perelman School of Medicine at the University of Pennsylvania, said, "These studies address the question of what may happen in the lungs, but they do not address the issue of transmissibility." Scientists know that part of Omicron's infection comes from its ability to evade antibodies, allowing it to spread more easily among vaccinated individuals compared to other variants. However, scientists suspect that Omicron may also have other biological advantages.
