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. 2023 Sep;28(36):2300048.
doi: 10.2807/1560-7917.ES.2023.28.36.2300048.

A standardised protocol for relative SARS-CoV-2 variant severity assessment, applied to Omicron BA.1 and Delta in six European countries, October 2021 to February 2022

Tommy Nyberg  1 , Peter Bager  2 , Ingrid Bech Svalgaard  2 , Dritan Bejko  3 , Nick Bundle  4 , Josie Evans  5 , Tyra Grove Krause  2 , Jim McMenamin  5 , Joël Mossong  3 , Heather Mutch  5 , Ajibola Omokanye  4 , André Peralta-Santos  6 , Pedro Pinto-Leite  6 , Jostein Starrfelt  7 , Simon Thelwall  8 , Lamprini Veneti  7 , Robert Whittaker  7 , John Wood  5 , Richard Pebody  9   10 , Anne M Presanis  1   9
Affiliations

A standardised protocol for relative SARS-CoV-2 variant severity assessment, applied to Omicron BA.1 and Delta in six European countries, October 2021 to February 2022

Tommy Nyberg et al. Euro Surveill. 2023 Sep.

Abstract

Several SARS-CoV-2 variants that evolved during the COVID-19 pandemic have appeared to differ in severity, based on analyses of single-country datasets. With decreased testing and sequencing, international collaborative studies will become increasingly important for timely assessment of the severity of new variants. Therefore, a joint WHO Regional Office for Europe and ECDC working group was formed to produce and pilot a standardised study protocol to estimate relative case-severity of SARS-CoV-2 variants during periods when two variants were co-circulating. The study protocol and its associated statistical analysis code was applied by investigators in Denmark, England, Luxembourg, Norway, Portugal and Scotland to assess the severity of cases with the Omicron BA.1 virus variant relative to Delta. After pooling estimates using meta-analysis methods (random effects estimates), the risk of hospital admission (adjusted hazard ratio (aHR) = 0.41; 95% confidence interval (CI): 0.31-0.54), admission to intensive care unit (aHR = 0.12; 95% CI: 0.05-0.27) and death (aHR = 0.31; 95% CI: 0.28-0.35) was lower for Omicron BA.1 compared with Delta cases. The aHRs varied by age group and vaccination status. In conclusion, this study demonstrates the feasibility of conducting variant severity analyses in a multinational collaborative framework and adds evidence for the reduced severity of the Omicron BA.1 variant.

Keywords: COVID-19; SARS-CoV-2; severity; study protocol; variant of concern; virulence.

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Conflict of interest statement

Conflict of interest: None declared.

Figures

Figure 1
Figure 1
Summary of the development and application of the study protocol and the statistical analysis code
Figure 2
Figure 2
Hazard ratios of hospital admissiona for COVID-19 cases infected with the Omicron BA.1 versus Delta variants, by country and pooled across countries using a fixed effect and a random effect model, in six European countries, October 2021–February 2022
Figure 3
Figure 3
Hazard ratios of admission to intensive care unita for COVID-19 cases infected with the Omicron BA.1 versus Delta variants, by country and pooled across countries using a fixed effect and a random effect model, in sixb European countries, October 2021–February 2022
Figure 4
Figure 4
Hazard ratios of deatha for COVID-19 cases infected with the Omicron BA.1 versus Delta variants, by country and pooled across countries using a fixed effect and a random effect model, in sixb European countries, October 2021–February 2022
Figure 5
Figure 5
Hazard ratios of hospital admissiona for COVID-19 cases infected with the Omicron BA.1 versus Delta variants, by age group, in six European countries, October 2021–February 2022
Figure 6
Figure 6
Hazard ratios of hospital admissiona for COVID-19 cases infected with the Omicron BA.1 versus Delta variants, by vaccination status in six European countries, October 2021–February 2022
See this image and copyright information in PMC

References

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Supplementary concepts