Omicron Found To Pose Lower Illness Risks

 

"LONDON -- People infected with the Omicron variant of coronavirus are at markedly lower risk of hospitalization than those who contracted earlier versions of the virus, new data from Scotland and South Africa suggest.

The data, from two real-life studies, offer promising signs that immunity as a result of vaccination or prior infection remains effective at warding off severe illness with the fast-spreading strain.

The findings begin to fill in unknowns around the severity of the disease caused by Omicron, a major variable critical to health authorities around the world as they gauge how to react to the new variant.

Scientists are still unsure how the positive findings around hospitalizations will stack up against another major variable: Omicron's much increased transmissibility. Both variables are likely to change depending on local conditions, such as the proportion of the population that has been vaccinated against Covid-19.

"This is a qualified good news story," said Jim McMenamin, incident director for Covid-19 at Public Health Scotland, and one of the authors of the Scottish study, at a briefing. "It's important we don't get ahead of ourselves. A smaller proportion of a much greater number of cases can still mean a substantial number of people that might experience severe Covid infections that could lead to hospitalization."

The University of Edinburgh study, drawing on the health records of 5.4 million people in Scotland, found the risk of hospitalization with Covid-19 was two-thirds lower with Omicron than with Delta. The new variant became dominant in Scotland last week.

A separate study published online by researchers at South Africa's National Institute for Communicable Diseases similarly found people infected with Omicron were 70% to 80% less likely to need hospital treatment than people infected with earlier variants, including Delta.

"In South Africa, this is the epidemiology. Omicron is behaving in a way that is less severe," Professor Cheryl Cohen, who heads the institute's center for respiratory diseases and meningitis, told reporters on a conference call.

The risk of severe complications in those who were admitted to the hospital, such as needing oxygen or intensive care, was also reduced with Omicron compared with other variants, the researchers in South Africa said.

These new studies, which haven't yet been peer-reviewed, shed light on the severity of illness Omicron causes. They offer new evidence that Omicron infections tend to be milder in populations with high levels of immunity, whether from vaccination or prior infection. In Scotland, 83.6% of people aged 12 and over have received two doses of vaccine, and 56.6% have received a third shot.

What is less clear is whether Omicron itself is intrinsically less virulent than earlier versions of the virus, which has killed at least 5.4 million people world-wide and caused close to 300 million known cases of Covid-19.

An analysis of recent Covid-19 cases in England by Imperial College London, also published Wednesday, suggested the risk of hospitalization with Omicron is only around 10% to 11% lower than Delta for someone who hasn't been vaccinated and never previously infected, highlighting the protection that persists against the new variant from vaccination or exposure to the virus.

"The overall picture we get of this virus as it moves through the community month by month and then eventually year by year will be a milder one. It doesn't mean the virus necessarily is any fundamentally less virulent. It just means we have built up a lot more protection in the population," said Neil Ferguson, a professor at Imperial College London who led the research.

South African scientists alerted the world to Omicron's existence in late November and since then it has been detected in more than 80 countries.

In the U.S., Omicron accounts for almost three-quarters of recent Covid-19 cases, according to the Centers for Disease Control and Prevention.

Scientists quickly learned the variant's dozens of mutations meant it was highly transmissible and adept at causing infections in people with some degree of immunity, including people who were vaccinated.

These new studies provide more information for modelers predicting the impact the variant will have.

"We don't have as many admissions to hospital as we were expecting, had Omicron been exactly the same as the Delta infection," said Chris Robertson, professor of public health epidemiology at the University of Strathclyde, who contributed to the Scottish study.

In 22,205 infections with Omicron, researchers in Scotland expected to see 47 hospital admissions based on their experience with Delta, but instead observed 15.

Both sets of researchers said more data are needed to build a more accurate picture.

Prof. Robertson said that the data from Scotland were very preliminary and the majority of the Omicron infections studied arose in people aged between 20 and 59 years old, who tend to suffer less severe Covid-19 than older people. South Africa's population is also younger on average than those of the U.S. and Europe.

"Overall the fact that we are seeing data now from two countries pointing in the same direction is encouraging," said Professor Aziz Sheikh who led the Scottish study. But he added that Omicron's increased transmissibility compared with Delta means that if there are many more infections -- the U.K. crossed a record 100,000 daily Covid-19 cases on Wednesday -- only a very small proportion of those ending up in hospital could put the state-run health service under huge pressure.

"That's the balancing act," Prof. Sheikh said.

The Scottish study also found that a booster shot provides less additional protection against symptomatic infection from Omicron than against Delta. Among people aged 50 and older who had recently received a booster, the risk of testing positive with Omicron was 57% lower than in those who had received their second dose at least six months earlier. For Delta, a booster reduced the risk of symptomatic infection by 88%.

Prior infections also appeared to be less protective against Omicron than Delta. The study found that 7.6% of all Omicron infections were possible reinfections, versus just 0.7% of Delta infections over the same period." [1]

1. Omicron Found To Pose Lower Illness Risks
Douglas, Jason; Roland, Denise. Wall Street Journal, Eastern edition; New York, N.Y. [New York, N.Y]. 23 Dec 2021: A.1.