Despite initial fears last November that genetic changes to the Omicron variant might spell disaster for humans, rodent studies that isolate the effects of Omicron in the body from the effects of Omicron infection after a vaccine or previous natural infection showed that Omicron is indeed a less deadly version of the virus with milder symptoms.
Initially, Omicron's genetic sequence concerned scientists. They found more than 30 mutations to its spike protein, some of which were found in Alpha and Delta and linked to increased infectivity and immune system evasion. Fortunately, Omicron is turning out to be a case where you can't judge how a virus will infect someone based on its genetic sequence alone.
Researchers infected hamsters and mice with Omicron and other variants to study Omicron's effects on the respiratory tract. Compared to the other variants, Omicron was less concentrated in the animals' lungs – at least ten times less concentrated. SARS-CoV-2's ability to damage lung tissue is thought to be largely responsible for its deadliness with previous variants.
Whereas previous variants were found to bind to a protein in the lung known as TMPRSS22, this isn't the case with Omicron, which doesn't bind so well to it. Instead, Omicron infects cells of the upper respiratory tract and has mutations known to enhance its ability to enter those cells and infect them, both findings that may, at least in part, explain why it's more contagious.
Another sign Omicron-infected rodents weren't as sick: they nearly maintained their body weight while the groups infected with other variants rapidly lost theirs.
As Dr. Robert Wachter, chairman of the department of medicine at the University of California, San Francisco puts it, "A case of Omicron compared to a case of Delta in a comparable person, comparable vaccination status, comparable age and risk factors is on the order of 60% to 70% less severe."
Disclaimer: While this article reports on scientific studies describing facets of the nature of the Omicron variant, it is important to note that it remains a dangerous and contagious viral infection that poses a grave health risk to the population. Get more facts about the Omicron variant from the University of Maryland Medical System.
Sources: Nature, Nature, Nature, WSJ, Nature Portfolio
