Latest data from U.K. suggests omicron less likely than delta to require hospitalization

Researchers looking at real-world coronavirus cases in Britain reported Wednesday that the omicron variant appears to be less severe than the once-dominant delta strain.

Early evidence from Scotland and England suggests that omicron is sending fewer people to the hospital with severe symptoms.

That surveillance tracks well with the latest observations from South Africa, where public health officials have reported that omicron is tending to result in milder illness. Scientists had not been sure whether that finding would hold elsewhere.

“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.

Public health 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 recorded in Britain exceeded 100,000 on Tuesday for the first time in the pandemic.

Prime Minister Boris Johnson has said his government is watching the data but would not call for stricter measures to fight 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 The study, which has not yet been peer reviewed, found that people infected with omicron were almost 60% less likely to enter the hospital than those infected with delta, the dominant strain around the world for much of 2021.

The Scottish scientists said 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% reduction in the odds of developing symptomatic covid. Boosters gave better protection against the delta variant – more than 80%.

The researchers estimated the potential for reinfection 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% less likely to go to an emergency room with severe symptoms and 40% less likely to be hospitalized overnight, when compared to 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 virus, “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.”

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 and, 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.