An analysis by the UK Health Security Agency has shown someone infected with the omicron variant of SARS-CoV-2 is estimated to be between 31% and 45% less likely to attend emergency care than if they had been infected with the Delta variant and 50-70% less likely to be admitted to hospital.
But the agency said the findings, which exclude people with previous SARS-CoV-2 infection, are preliminary and highly uncertain because of the small numbers of hospital cases of omicron, an inability to effectively measure all previous infections, and the limited spread of omicron into older age groups.
It also emphasized that although a smaller proportion of people with omicron could end up in hospital than with previous variants, the actual number becoming seriously ill and needing hospital care could be huge, because of the variant’s increased transmissibility.
The analysis, published on December 23, 2021, also found that omicron was more likely than previous variants to reinfect people who have previously had COVID-19, with 9.5% of those infected having a history of past infection. This figure is likely to be an underestimate because of some people being unaware that they had had asymptomatic prior infections, meaning they are not reported in the numbers.
It’s still too early to estimate vaccine effectiveness against hospital admissions, but the agency said that this was more likely to be sustained, particularly after a booster.
The agency’s findings are consistent with three recent studies, not yet peer reviewed, from researchers in England, Scotland, and South Africa, which all concluded that omicron carried a lower risk of hospital admission than Delta.