Omicron covid cases are less severe than Delta, new studies say
Dec 22nd 2021AS THE OMICRON wave of covid-19 washes over Europe and America, it is only a matter of time before the variant breaks over the rest of the world. First spied in South Africa, Omicron had been detected in 106 countries, and counting, by December 22nd. The world has been here before, with new variants causing record peaks in cases. The hope this time around, however, is that layers of immunity from past infections and vaccines—layers which now exist, in some combination, in every country on Earth—will make serious Omicron infections a lot less common than serious infections of other variants were. Three new studies suggest that hope will be borne out. In one, published on December 22nd, researchers from Imperial College London pored over early data on Omicron in England. They found that people recorded as infected with the variant are about 15-20% less likely to seek hospital care and 40% less likely to be admitted for a night or longer than those with Delta. They had shorter hospital stays, too. That Omicron cases are, on average, less severe is partly due to their being more likely than Delta cases to be reinfections (because of Omicron’s ability to dodge some of the protection conferred by a previous bout). Among people who have acquired no immunity either from infection or vaccination, Omicron’s propensity to lead to hospital admission is only 11% lower than Delta’s, the researchers reckon. Previous infection, however, turns out to cut the risk of hospital admission by 55-70%. By some estimates, about half of people in England have had covid at some point, a substantial layer of protection from severe disease for those who catch Omicron.A second study, released on the same day, came from Scotland, one of the first places with a large wave of the new variant. Researchers there examined a cohort of people with confirmed covid infections. They found that far fewer Omicron cases ended in hospital stays than would have been expected if the variant had been as virulent as Delta (after accounting for whether infected people had been vaccinated and other characteristics). A caveat is that the results apply mainly to covid patients under 60, because in Scotland the variant is yet to spread widely among the old. The results are nonetheless encouraging. The risk of an Omicron infection requiring hospital care is a third of that for Delta. The third study, published the previous day, is from South Africa, where the Omicron wave of infections is already cresting. Researchers there found that Omicron cases were 80% less likely to need hospital admission than non-Omicron cases (mostly Delta), after adjusting for things that affect the chances of developing severe disease, such as age and chronic illness. All three studies examined the same question using different data, methods and groups of people. They differ in the magnitude of their findings, as you would expect with such early research. But they all point in the same direction: that Omicron appears to be less severe than Delta. It is, however, a lot more infectious. In the coming days, modellers will be busy calculating how infection and severity offset each other, in order to advise governments on what hospitals should expect in the new year. Many of them are already overstretched.All our stories relating to the pandemic can be found on our coronavirus hub. You can also find trackers showing the global roll-out of vaccines, excess deaths by country and the virus’s spread across Europe.