4 studies on Omicron: What they reveal so far

FOUR STUDIES: Omicron is a fast-moving variant. The highly infectious variant's spread is the question of the moment. Four research teams have separately published results of studies on Omicron vs Delta.

PRELIMINARY: Preliminary data suggest Omicron-infected people face less risk of hospitalisation and less severity, if hospitalised. Due to the small sample size of patient data used in the studies, scientists are still not sure whether their findings would hold elsewhere.

INITIAL FINDINGS: By Wednesday (December 22, 2021), the four studies were out as “pre-prints” — two separate studies were conducted in the UK, and one each in Hong Kong and South Africa. They basically confirm each other’s findings. Still, conclusions are “preliminary”, i.e. need further confirmation in larger studies.

SCOTTISH STUDY — 60% REDUCTION: The research from Scotland, led by the scientists at the University of Edinburgh, found that people infected with the Omicron variant were almost 60% less likely to enter the hospital than those infected with Delta, the once globally-dominant variant now being overtaken rapidly.

EARLY DATA: Though the UK national data analysed in the Scottish study is considered “early” and need further investigation, it does point to Omicron being associated with a two-thirds (60%) reduction in the risk of COVID-19 hospitalisation when compared to Delta, according to results of the study published by the University of Edinburgh.

PROTECTION FROM SYMPTOMATIC INFECTION: The Scottish scientists said that recently-vaccinated people appear to have some protection against symptomatic infection from Omicron, though less so than against Delta. A third dose (or booster of an mRNA shot) led to a 57% reduction in the risk of developing symptomatic COVID-19. Boosters gave better protection against the delta variant — more than 80% — the researchers found.

10X REINFECTION RISK WITH OMICRON: The Edinburg researchers estimated the potential for reinfection is 10 times with Omicron compared to Delta. The numbers they worked with, though small, were “statistically significant” — i.e. that if Omicron acted the same as Delta, they would expect 47 people to have been hospitalised already against the actual number of only 15. So while there were not enough Omicron infections and hospitalisations among those over 60 years to reach confident conclusions, they expected the overall trend would hold.

IMPERIAL COLLEGE LONDON STUDY: The Imperial College's study, published December 22, 2021, also found that Omicron leads to less severe COVID in England. That research team, 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 hospitalised overnight, when compared with those infected by Delta. Ferguson said: “Our analysis shows evidence of a moderate reduction in the risk of hospitalisation” associated with the Omicron compared with Delta. “However, this appears to be offset by the reduced efficacy of vaccines against infection with the omicron variant.”

EXPERT REACTION: Scientists not involved in the two UK studies expressed relief that Omicron was not worse — and very likely less bad — than Delta. Raghib Ali, a clinical research associate and epidemiologist at the University of Cambridge, said both reports were “encouraging.” “And while further data is needed to confirm these studies, the worst-case scenarios that were presented last week can safely be excluded.”

HONG KONG STUDY: On December 15, 2021, a Hong Kong team published their study showing why Omicron leads to an astonishingly high transmissibility — it multiplies up to 70 times quicker than earlier strains within the lower airways of human lungs. The Omicron variant may now account for most of COVID infections exploding around the world.

OMICRON VIRUS PARTICLES: Omicron virus particles (orange) amass in vesicles (a small fluid-filled bladder/sac/cyst/vacuole within the body) and are released on the surface of monkey cells. The Hong Kong study used a technique developed in 2007 involving use of ex-vivo cultures of the respiratory tract to investigate avian flu and MERS. It has been applied to understand Omicron, and it differs in transmission and disease severity from other SARS-CoV-2 variants.

REPLICATION: The Hong Kong team found that the Omicron variant replicates at an astonishingly faster rate than the original SARS-CoV-2 virus and Delta variant in the human bronchus. Photo shows an enlarged view of human bronchus tissue infected with the Omicron variant of the SARS-CoV-2 coronavirus (in red) in laboratory research from a team in Hong Kong. 

70x HIGHER REPLICATION 24 HOURS POST-INFECTION: The Hong Kong researchers found that at 24 hours post-infection, the Omicron variant replicated around 70 times higher than Delta and the original SARS-CoV-2 virus. In contrast, they also found that the Omicron variant replicated less efficiently (more than 10 times lower) in the human lung tissue than the original SARS-CoV-2 virus. In other words, Omicron replicates less well deep inside human lungs. This, the researchers hypothesise, may suggest lower severity of disease.

SOUTH AFRICA STUDY: Another pre-print study, published by researchers from South Africa also on Wednesday, shows 80% less hospitalisation with Omicron, 30% less severe than Delta. “In South Africa, this is the epidemiology: Omicron is behaving in a way that is less severe,” said Professor Cheryl Cohen of the NICD, one of the authors. “Compellingly, together our data really suggest a positive story of a reduced severity of Omicron compared to other variants.” File photo shows technicians conduct antibody testing at the African Health Research Institute in Durban, South Africa.

NO FINAL VERDICT ON OMICRON’S SEVERITY: South Africa’s National Institute for Communicable Diseases (NICD) study conducted with major universities compared South African Omicron data from October and November 2021 with data about Delta between April and November 2021. Still, the authors of both the Hong Kong and South African studies included caveats and cautioned against jumping to conclusions — saying high population immunity was a possible factor.