Omicron COVID-19 variant more transmissible but causes less severe illness than Delta, British studies find

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A pair of British studies has found that the Omicron variant causes much less severe illness than Delta and that the risk of hospitalization is up to two-thirds lower.

However, the researchers cautioned that because Omicron is far more transmissible, the lower hospitalization rate will likely be offset by soaring COVID-19 case numbers as the wave of infections builds.

“It’s good news as far as it goes,” said Mark Woolhouse, a professor of infectious-disease epidemiology at the University of Edinburgh who participated in one of the studies. “These results could have come out a lot worse with a lot higher levels of severity, and they haven’t. That is good news but that only takes us so far.”

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That point was driven home on Wednesday as Britain exceeded 100,000 daily COVID-19 infections for the first time. A total of 106,122 cases were reported by the U.K. Health Security Agency, a new record for the pandemic. Daily infections have increased nearly 60 per cent in the past week largely because of the Omicron variant, which is now the dominant mutation in much of the country.

However, so far the number of people admitted to hospital with COVID-19 has not been rising as quickly. There are currently 8,008 people in hospital across Britain. That’s the highest total in a month but it’s still almost five times lower than the number of hospitalizations last January when the country faced a peak of infections caused by the Alpha variant.

The first study released Wednesday came from researchers at a group of universities in Scotland who have been conducting real-time analyses of the pandemic by regularly tracking 5.4 million anonymized health records provided by Public Health Scotland.

They examined around 22,000 Omicron cases and 119,000 Delta infections reported in Scotland between Nov. 1 and Dec. 19. The scientists said that if Omicron behaved in the same manner as Delta, they would have expected 47 hospitalizations out of the 22,000 cases. However, there are currently only 15 people in hospital with the variant. “These early national data suggest that Omicron is associated with a two-thirds reduction in the risk of COVID-19 hospitalization when compared to Delta,” the study concluded.

Aziz Sheikh, a professor of primary-care research and development at the University of Edinburgh, said the Scottish findings largely backed up a similar study from South Africa that found that people with Omicron were 70 per cent less likely to develop severe illness compared to those who contracted Delta. “The fact that we are seeing data now from two countries pointing in the same direction is encouraging,” Dr. Sheikh said Wednesday.

He added that the study will soon be published in a medical journal and that the results have been forwarded to the World Health Organization, the Scottish government and the British government’s scientific advisory committee.

“This is a qualified good-news story,” added Jim McMenamin, national COVID-19 incident director at Public Health Scotland. “It’s important that we don’t get ahead of ourselves. A smaller proportion of a much greater number of cases that might ultimately require treatment can still mean a substantial number of people who might experience severe COVID-19 infections that could lead to potential hospitalization.”

The second study came from researchers at Imperial College London who found that, on average, people with Omicron were up to 25 per cent less likely to seek medical attention compared to those with Delta. They were also up to 45 per cent less likely to be admitted to hospital for one day or longer.

The Imperial team, which is part of the WHO collaborating centre for infectious-disease modelling, also addressed a key unanswered question about Omicron: whether it is intrinsically less virulent than Delta. It’s difficult to measure because most of the population in countries such as Britain have developed some immunity to all variants of the virus through vaccination or infection, which could explain why Omicron is causing less severe illness. The Imperial researchers estimated that someone who had no immunity would be about 10 per cent less likely to be hospitalized if they had Omicron, which suggested that it was not substantially weaker than Delta.

Neil Ferguson, an infectious-disease professor at Imperial College, said the overall findings were good news but they wouldn’t change current models that suggest British hospitals could become overwhelmed with Omicron cases. “Even with a 30- to 40-per-cent reduction in hospitalization, if cases get 30 to 40 per cent larger you’re back where you were before,” he said. “The key issue is predicting how high the peak will be.”

Scientists also said that so far Omicron has been largely limited to younger age groups and that it’s not clear how it will effect older people. “It’s only very recently that a relatively small number of elderly people have tested positive with Omicron,” said Chris Robertson, professor of public-health epidemiology at the University of Strathclyde. “If it turns out that people who are elderly with [Omicron] actually have a more severe infection, our counts will be an underestimation.”

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