People with Omicron are less likely to be hospitalised than those with Delta, three studies have suggested.
Questions about Covid-19 variant’s virulence are at the heart of scientific and political debate in many countries, as governments grapple with how to respond to the spread of the variant while researchers race to understand it.
On Wednesday, three pieces of research were published which could influence how lives are led in the short-term.
England
Research from Imperial College London indicates that people with PCR-confirmed Omicron are 15 to 20% less likely to need admission to hospital, and 40 to 45% less likely to require a stay of one night or more.
However, researchers have added that although Omicron appears less severe, it is more transmissible partly because the current crop of coronavirus vaccines are less effective against it.
Professor Neil Ferguson, from Imperial College London, said: “Our analysis shows evidence of a moderate reduction in the risk of hospitalisation associated with the Omicron variant compared with the Delta variant.
“However, this appears to be offset by the reduced efficacy of vaccines against infection with the Omicron variant.
“Given the high transmissibility of the Omicron virus, 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.”
The Imperial study, which has not yet been peer-reviewed, was based on PCR-confirmed coronavirus cases among both vaccinated and unvaccinated people recorded in England between December 1 and 14.
This sample included 56,000 Omicron cases and 269,000 Delta cases.
Scotland
Scientists in a Scotland-wide study called Early Pandemic Evaluation and Enhanced Surveillance of Covid-19 have said Omicron is associated with a two-thirds reduction in the risk of hospitalisation compared with Delta.
Dr Jim McMenamin, the national Covid-19 incident director for Public Health Scotland, labelled the findings of the Scotland study another “qualified good news story”, but said that it was “important we don’t get ahead of ourselves”.
He said: “The potentially serious impact of Omicron on a population cannot be underestimated.
“A smaller proportion of a much greater number of cases that might ultimately require treatment can still mean a substantial number of people who may experience severe Covid infections that could lead to potential hospitalisation.”
Authors of the Scotland paper, which is yet to be peer reviewed, said if Omicron had been like the Delta variant in Scotland they would have seen around 47 people in hospital suffering from the virus but, so far, there are only 15.
Professor Mark Woolhouse, of the University of Edinburgh, said the data is heavily caveated because it is based on a small number of cases which did not include many people aged over 65.
The Omicron strain is now the dominant type of virus in Scotland, with cases of the variant surging across the United Kingdom.
South Africa
A South African study suggests reduced risks of hospitalisation and severe disease in people infected with the Omicron coronavirus variant versus the Delta one – though the authors say some of that is likely due to high population immunity.
The new study, which has not been peer-reviewed, sought to assess the severity of disease by comparing data about Omicron infections in October and November with data about Delta infections between April and November, all in South Africa.
The analysis was carried out by a group of scientists from the National Institute for Communicable Diseases (NICD) and major universities including University of the Witwatersrand and University of KwaZulu-Natal.
They used data from four sources: national Covid-19 case data reported to the NICD, public sector laboratories, one large private sector lab and genome data for clinical specimens sent to NICD from private and public diagnostic labs across the country.
The authors found the risk of hospital admission was roughly 80% lower for those infected with Omicron compared with Delta, and that for those in hospital the risk of severe disease was roughly 30% lower.
However, they included several caveats and cautioned against jumping to conclusions about the intrinsic characteristics of Omicron.
“It is difficult to disentangle the relative contribution of high levels of previous population immunity versus intrinsic lower virulence to the observed lower disease severity,” they wrote.