LONDON — Researchers looking at real-world coronavirus cases in Britain reported Wednesday that the omicron variant of the coronavirus appears to be less severe than the once-dominant delta strain.
“This is a qualified good-news story,” said Jim McMenamin, national covid-19 incident director at Public Health Scotland and one of the co-authors of the Scottish study.
Experts remain worried that a sudden, massive surge of a highly infectious but less virulent omicron variant could still flood hospitals with very sick patients.
New daily coronavirus cases reported in Britain exceeded 100,000 on Wednesday for the first time in the pandemic. But the United Kingdom is also furiously giving people their third dose or booster jab — administering almost a million shots on Tuesday.
Prime Minister Boris Johnson has said his government is watching the data but would not call for stricter measures to fight the spread until after Christmas at the earliest.
The early research from Scotland was led by the scientists at the University of Edinburgh, in a well-vaccinated population not too different from the United States. The power of the study lay in the wealth of data kept by the National Health Service in Scotland — records of vaccination status, age, gender, underlying health conditions and coronavirus infection for nearly 98 percent of the Scottish population.
The study, which has not yet been peer reviewed, found that people infected with the omicron variant were almost 60 percent less likely to enter the hospital than those infected with delta, the globally dominant variant that is being eclipsed rapidly.
The Scottish scientists said that recently vaccinated people appear to have some protection against symptomatic infection from omicron but less so than against delta. A third dose or booster of an mRNA vaccine was associated with a 57 percent reduction in the odds of developing symptomatic covid-19. Boosters gave better protection against the delta variant — more than 80 percent.
The researchers estimated the potential for reinfection is 10 times more likely with omicron than with delta.
The numbers they were working with were small but statistically significant, they said — if omicron acted the same as delta, they would expect 47 people to have been admitted to hospital so far. Currently, there are only 15.
The scientists said there were not enough omicron infections and hospitalizations among those over 60 years to reach confident conclusions, but they expected the overall trend would hold.
The evidence that omicron was causing less severe illness in England came out of Imperial College London.
That group, led by Neil Ferguson, reported that those infected by omicron were 15 to 20 percent less likely to go to an emergency room with severe symptoms and 40 percent less likely to be hospitalized overnight, when compared with those infected by delta.
Ferguson also urged caution.
“Our analysis shows evidence of a moderate reduction in the risk of hospitalization associated with the omicron variant compared with the delta variant,” he said. “However, this appears to be offset by the reduced efficacy of vaccines against infection with the omicron variant.”
Ferguson stressed that given the high transmissibility of the omicron variant, “there remains the potential for health services to face increasing demand if omicron cases continue to grow at the rate that has been seen in recent weeks.”
British scientists not involved in the two studies expressed relief that omicron was not worse — and very likely less bad — than delta.
Raghib Ali, a clinical research associate and epidemiologist at the University of Cambridge, called the reports “encouraging.”
“This is the key data point we needed to estimate the likely peak and total number of admissions in the coming weeks,” Ali told science reporters. “And while further data is needed to confirm these studies, the worst-case scenarios that were presented last week can safely be excluded.”
South Africa’s top infectious-disease scientist, who has been leading the country’s pandemic response, told The Washington Post on Wednesday that the country had rapidly passed the peak of new omicron cases. Judging by preliminary evidence, he expected “every other country, or almost every other, to follow the same trajectory.”
South Africa, though, has a younger average age than countries in Europe or the United States, and it was not in the middle of a delta surge when omicron arrived.
Max Bearak in Nairobi contributed to this report.
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