Two new British studies provide some first clues that the Omicron variant may be less virulent than the Delta.
Scientists point out that even if the results of these early studies hold up, any reduction in severity must be weighed against the fact that Omicron spreads much faster than Delta and is more likely to evade vaccines. The large number of infections could still overwhelm hospitals.
Still, the new studies released Wednesday appear to bolster previous research that suggests Omicron may not be as harmful as the Delta variant, said Manuel Ascano Jr., a Vanderbilt University biochemist who studies viruses.
“Cautious optimism is perhaps the best way to look at it,” he said.
An analysis by the COVID-19 response team at Imperial College London estimated the risks of hospitalization for Omicron cases in England, and it found that those infected with the Omicron variant are around 20% less likely to go to hospital than those infected with the Delta variant, and 40% less likely to be hospitalized overnight or longer.
This analysis included all cases of COVID-19 confirmed by PCR tests in England during the first two weeks of December in which the variant could be identified: 56,000 cases of Omicron and 269,000 cases of Delta.
A separate study in Scotland, conducted by scientists at the University of Edinburgh and other experts, suggested that the risk of hospitalization was 66% lower with Omicron than with Delta. But that study pointed out that the nearly 24,000 cases of Omicron in Scotland were mostly among young adults between the ages of 20 and 39. Young people are much less likely to develop severe cases of COVID-19.
“This national survey is one of the first to show that Omicron is less likely to result in hospitalization for COVID-19 than Delta,” the researchers wrote. Although the results are preliminary observations, “they are encouraging,” the authors wrote.
The results have not yet been peer reviewed, however.
Manuel Ascano noted that these studies have limitations. For example, the results are specific to a certain point during a rapidly changing UK situation and other countries may not fare the same.
Matthew Binnicker, director of clinical virology at the Mayo Clinic in Rochester, Minnesota, said in the Scottish study the percentage of young people was almost twice as high for the Omicron group as it was for the Delta group, which “would have could bias the conclusions ”.
He nevertheless said the data was interesting and suggested that Omicron could lead to less serious illness. But he added, “It’s important to point out that while Omicron has a much higher transmission rate than Delta, the absolute number of people requiring hospitalization could increase further, despite less severe illness in most cases. “
Data from South Africa, where the variant was first detected, also suggested that Omicron might be less dangerous. Salim Abdool Karim, clinical infectious disease epidemiologist in South Africa, said earlier this week that the hospital admissions rate was much lower for Omicron than it was for Delta.
“Our overall admission rate is in the range of 2% to 4% compared to previously, where it was closer to 20%,” he said. “So even though we see a lot of cases, very few are admitted. “
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