New Data Suggests Omicron More Contagious But Less Severe Than Delta


So far, the theory that the Omicron variant causes less severe disease than the Delta variant has been largely anecdotal. Now, new real-world studies from Scotland and England shows that Omicron does not lead to as much hospitalization as Delta. This is consistent with the latest reports from South Africa that say Omicron causes milder disease.

“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.

On December 22, new daily COVID-19 cases in Britain were over 100,000 for the first time since the beginning of the pandemic. The UK has accelerated their dosing of booster shots, giving out almost a million on Tuesday, December 21.

The Scottish study was led by researchers at the University of Edinburgh, which leveraged data from the National Health Service in Scotland, which included vaccination status, age, gender, comorbidities and COVID-19 infection for almost 98% of the country’s population. The research found that recently vaccinated individuals seem to have some protection against symptomatic infection from Omicron, but less than what was observed against Delta. A booster shot of the Moderna or Pfizer-BioNTech mRNA vaccine was linked to a 57% decrease in the likelihood of developing symptomatic COVID-19 from Omicron, but about 80% against Delta.

They also estimated that the possibility for reinfection was 10 times higher with Omicron than Delta. However, their data sample wasn’t that large but was statistically significant, working on assuming that Omicron behaved the same as Delta. With that assumption, they would expect 47 people to have been admitted to the hospital with Omicron, but so far there has only been 15. They also say there haven’t been enough Omicron infections and hospitalizations in people over the age of 60 to be completely confident in the conclusions.

study out of Imperial College London provided the data suggesting Omicron was tied to less severe disease. Their research found that people infected with Omicron were 15% to 20% less likely to end up in an emergency room with severe symptoms and 40% less likely to be hospitalized overnight compared to people with Delta infections. But, as with the Scottish data, the researchers are being conservative on their conclusions.

“Our analysis shows evidence of a moderate reduction in the risk of hospitalization associated with Omicron variant compared with the Delta variant,” said Neil Ferguson, who led the Imperial College London research team. “However, this appears to be offset by the reduced efficacy of vaccines against infection with the Omicron variant.”

He also noted that because the Omicron variant is so infectious, “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.”

Raghib Ali, a clinical research associate and epidemiologist at the University of Cambridge, who was not involved in the studies, said, “This is the key data point we needed to estimate the likely peak and total number of admissions in the coming weeks. And while further data is needed to confirm these studies, the worst-case scenarios that were presented last week can safely be excluded.”

Back to news