Media release

From: The Lancet

Nationwide study of COVID in Denmark shows people with omicron variant 36% less likely to be hospitalised than those with delta variant

• Reduced risk of hospitalisation with omicron both among unvaccinated and vaccinated suggest an inherently reduced severity of infections with omicron compared with delta

*Note: this paper is being presented at the European Congress of Clinical Microbiology & Infectious Diseases (ECCMID) and is being published in The Lancet Infectious Diseases.  Please credit both the congress and the journal in your stories*

New research presented at this year’s European Congress of Clinical Microbiology & Infectious Diseases (ECCMID 2022, Lisbon 23-26), and published in The Lancet Infectious Diseases shows that people infected with the omicron variant of SARS-CoV-2 are 36% less likely to be hospitalised then those with the delta variant, with the reduced risk observed among both unvaccinated and vaccinated. The study is by Dr Peter Bager, Statens Serum Institut, Copenhagen, Denmark, and colleagues.

In this observational cohort study, the authors included all PCR confirmed cases of SARS-CoV-2 infection in Denmark, with samples taken between Nov 21 (date of first omicron-positive sample) and Dec 19, 2021. Individuals were identified in the national COVID-19 surveillance system database, which included results of a variant specific PCR test that detected omicron cases, and data on SARS-CoV-2 related hospitalisations.

Among the 188 980 individuals with SARS-CoV-2 infection, 38 669 (20.5%) had the omicron variant. Overall, 124 313 (66%) of 188 980 individuals were vaccinated, and vaccination was associated with a 76% lower risk of hospitalisation (71% lower risk for omicron cases, 76% lower risk for delta), compared with cases with no doses or only one dose of vaccine (in this study, people with zero or only one dose of vaccine were classified in one group as unvaccinated because very few were infected or hospitalised after only one dose).

A total 222 (0.6%) of 38 669 omicron cases were admitted to hospital compared with 2213 (1.5%) of 150 311 delta cases. After adjustment for confounding, omicron infection was associated with a 36% lower risk ratio of hospitalisation compared with delta variant. When studying the effect of vaccination, the authors found that the reduced risk of hospitalisation for omicron versus delta was 43% for zero or one dose of vaccine, 29% for those who received two doses, and 50% for those who received three doses.

Compared with individuals with delta, individuals with omicron were younger, had less comorbidities, and were more often previously infected with SARS-CoV-2. Among hospitalised cases, a similar pattern was observed for omicron compared with delta with regards to age, comorbidity, and reinfection. Hospitalised omicron cases were made up of more women (61%) than men (39%), whereas hospitalised delta cases were 51% men and 49% women (see table 1 in full paper).

The authors conclude: “We found a significantly lower risk of hospitalisation with omicron infection compared with delta infection among both vaccinated and unvaccinated individuals, suggesting an inherent reduced severity of omicron. Our results could guide modelling of the effect of the ongoing global omicron wave and thus health-care system preparedness.”

The Lancet Infectious Diseases: Risk of hospitalisation associated with infection with SARS-CoV-2 omicron VOC versus delta VOC in Denmark: an observational cohort study– to be presented at a special Lancet journals COVID-19 session in Hall A of the European Congress on Clinical Microbiology & Infectious Diseases (ECCMID 2022) on Sunday April 24 at 16.15-18.15 Lisbon/UK time (WEST time zone).