New Omicron Studies Help Explain Why Variant Is Mild but Spreads Fast
The threat posed by the Omicron variant has now come into sharper focus, with recent clinical data and laboratory studies lending support to early reports suggesting that it is milder but more transmissible than other variants of the new coronavirus. “It spreads very, very fast, but it doesn’t appear to have the virulence or machismo to really pack as much of a wallop as the Alpha or Delta variants,” James Musser, chairman of Houston Methodist Hospital’s pathology and genomic medicine department and the leader of a new study of Omicron infections, said of the variant.
Recent laboratory studies suggest that Omicron’s lower virulence may reflect its apparent tendency to thrive in cells in the upper respiratory tract rather than in the lungs, where Covid-19 infections can cause potentially fatal breathing problems. Experiments on human respiratory tissues conducted recently at the University of Cambridge and the University of Hong Kong showed that Omicron prefers to infect cells in the bronchi, the tubes that connect the windpipe to the lungs, while the Delta variant better infects and replicates in lung tissue.
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The findings align with clinical results reported from South Africa, where Omicron was first identified in November. “We’re just not seeing patients admitted with Covid pneumonia and lung complications” that often accompany the most severe cases, said Waasila Jassat, a public health specialist at the National Institute for Communicable Diseases in Johannesburg.
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Omicron’s spike shares mutations spotted in earlier variants that are known to bind virus particles more tightly to cells, a process that Dr. Menachery likened to a key fitting a lock. Omicron also has two mutations, H655Y and P681H, that are known to boost the virus’s ability to enter cells, Dr. Menachery said.
Despite these recent findings, scientists have yet to answer many questions about Omicron, which has now caused outbreaks in more than 100 countries. For example, it isn’t yet clear how the course of symptomatic Omicron infections differs in unvaccinated people and those who have some immunity from vaccination or prior infection, though early reports suggest that the infections are milder in people with prior immunity. Similarly, researchers said it’s too soon in the current surge to conclude that Omicron is less lethal than other variants—though scientists said the comparatively low hospitalization rates and reduced need for breathing support associated with the variant mean that is likely the case.
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People infected with Omicron are less likely to need hospitalization or intensive care than those who have the Delta variant, according to recent studies of clinical data by Dr. Musser and other researchers. “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% or 70% less severe,” Dr. Wachter said... As they learn more about Omicron, doctors and public health officials continue to urge Americans to get vaccinated and boosted and to continue with masking and social distancing.
https://www.wsj.com/articles/new-omicron-studies-help-explain-why-the-variant-is-mild-but-spreads-fast-11641637803 (subscription)
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