Review 1: "Outcomes of SARS-CoV-2 Omicron infection in residents of Long-Term Care"

RR:C19 Evidence Scale rating by reviewer:

• Reliable. The main study claims are generally justified by its methods and data. The results and conclusions are likely to be similar to the hypothetical ideal study. There are some minor caveats or limitations, but they would/do not change the major claims of the study. The study provides sufficient strength of evidence on its own that its main claims should be considered actionable, with some room for future revision.

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Review:

In this paper, the authors evaluate the risk of hospitalization and death between Delta and Omicron SARS-CoV-2 variants in a cohort of Long-Term Care facilities in England. This paper contributes to the existing knowledge that Omicron is less severe than Delta, providing additional evidence in an especially frail population subset. 

The authors use a screening program in England that routinely tests individuals in LTCF; this strengthens the data as changes in testing policies can influence severity estimates. The definitions for hospitalization and death have some limitations because they can lead to misclassifying the outcome (it is not clear that the COVID-19 was the leading cause for admission or death). However, this method has been used before, misclassification is probably balanced between the Delta and Omicron groups.  

Another limitation of this study is that 20% of the tests done in LTCF could not be linked to hospitalization and death records. That could introduce a selection bias and the authors should explain if this non/linked population differs from the linked population. 

The methods are appropriate to answer the research questions. Still, they could benefit from making the model equation more explicit and giving the estimated prevalence of Delta and Omicron at the cut/off date 12-13 December 2021 and some guidance to the reader on how fast the Delta Omicron transition occurred.

Finally, some suggested papers to cite related to the research question can add depth to the discussion of results.   

Paper on outcomes during the Delta wave in LTCF

Suetens C, Kinross P, Berciano PG, Nebreda VA, Hassan E, Calba C, Fernandes E, Peralta-Santos A, Casaca P, Shodu N, Dequeker S. Increasing risk of breakthrough COVID-19 in outbreaks with high attack rates in European long-term care facilities, July to October 2021. Eurosurveillance. 2021 Dec 9;26(49):2101070.

Paper about the risk of hospitalization of Omicron

Peralta-Santos A, Rodrigues EF, Moreno J, Ricoca V, Casaca P, Fernandes E, Gomes JP, Ferreira R, Isidro J, Pinto M, Borges V. Omicron (BA. 1) SARS-CoV-2 Variant Is Associated With Reduced Risk of Hospitalization and Length of Stay Compared With Delta (B. 1.617. 2).