New studies suggest that Omicron infections are less severe than Delta infections

December 22, 2021 – People who get COVID-19 infections caused by Omicron are less likely to need hospital care than those infected Delta variant, according to two large new studies from the UK and South Africa.

The findings, published before the peer review, add to previous evidence that Omicron – although highly contagious – may result in less severe symptoms than its predecessors.

“This helps us quantify how less serious Omicron is than Delta, and it seems to reduce the risk of hospitalizations by 40 to 75%, adjusted for many factors, which is very good,” said Eric Topol, MD, editor-in-chief. CEO of Medscape and cardiologist at the Scripps Research Translational Institute in La Jolla, CA.

The first analysis, conducted by the World Health Organization Infectious Diseases Modeling Center and Imperial College London, found that overall people infected with Omicron had about a 20% reduced risk of needing any hospital care for their infections and a 40% lower risk of staying in hospital overnight, compared to those infected Delta.

Meanwhile, people who became infected again – meaning they infected Omicron after recovering from a previous COVID-19 infection – had a 50% -60% lower risk of needing hospital care, probably reflecting the benefits of a previous immunity against the same family of viruses.

The study included all individuals with confirmed COVID-19 polymerase virus in the UK during the first two weeks of December – approximately 56,000 cases of Omicron and 269,000 Delta infections.

The another study, from researchers from the National Institute of Infectious Diseases in South Africa, included more than 29,000 cases of COVID-19 that had laboratory results highly suggestive of Omicron infections. Compared with people infected with the Delta variant, those with presumed Omicron infections were about 70% less likely to have severe disease.

Although the news is full of hope for individuals, at the population level, health systems may still be under stress, the study authors warned.

“Given the high portability of the Omicron virus, there is still the possibility that health services may face increasing demand if Omicron cases continue to rise at the rate seen in recent weeks,” said study author Neil Ferguson, Ph.D., who studies how contagious diseases spread to Imperial College London.

The study’s authors say their findings are specific to the UK and South Africa, where a significant portion of the population has some immune protection against past infections. In other words, it may not apply to countries where fewer people have been vaccinated or recovered from the COVID-19 attack.