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Delta variant and its risk of hospital admission

The Delta variant of the SARS-CoV-2 virus is quite worrisome, but it has been debated whether, per se, it carries a higher risk of hospitalization beyond being a more contagious variant than the previous ones. A rigorous new study shows a doubling of the hospitalization rate for this variant. The study is conducted by the University of Cambridge and the English health service, Public Health England.

Background

The delta variant of SARS-CoV-2 (known as B.1.617.2)was first detected in England in March 2021. Since then it has quickly become the predominant lineage due to its high transmissibility. This variant is suspected to be associated with more severe disease than the previously dominant alpha variant (B.1.1.7).

A new study (https://doi.org/10.1016/S1473-3099(21)00475-8) sought to characterize the severity of this variant compared to the alpha variant by determining the relative risk of hospital care outcomes.

Methods

A cohort study was used to carry out this work. A cohort study is a type of observation and analysis research in which a comparison is made of the frequency of occurrence of an event between two groups, one of which expresses an event that is not present in the other.

This study was conducted among all COVID-19 patients in England between March 29 and May 23, 2021, using patients who were identified as infected with the alpha or delta variant of SARS-CoV-2 through whole genome sequencing. Individual-level data from these patients were linked to routine health care datasets on vaccination, emergency care assistance, hospital admission, and mortality.

We compared the risk of hospital admission and emergency care attendance among patients with sequencing-confirmed delta and alpha variants for the entire cohort and by subgroups of vaccination status.

Results

Data were obtained at the individual level from 43,338 COVID-19 positive patients (8,682  with the delta,  34,656  with the alpha; median age 31 years [Inter quartile range 17 years to 43 years]) were included in this analysis.  

Of these patients studied, 196 (2.3%) patients with the delta variant versus 764 (2.2%) patients with the alpha variant were admitted to hospital within  14 days of sampling (HR, Hazard Risk) 2.26). In addition, 498 (5.7%) patients with the delta variant versus 1448 (4.2%) patients with the alpha variant were admitted to hospital or attended emergency care within 14 days.

Most patients were not vaccinated (32,078 [74.0%] in both groups). The risk indices for patients vaccinated with the delta versus the alpha (HR adjusted for hospital admission 1.94 and for hospital admission or emergency care 1.58) were similar to the HR for unvaccinated patients but the accuracy for the vaccinated subgroup was low. Precision  is the ability of a study to give the same result in different measurements made under the same conditions or to give the desired result accurately.

Interpretation

This large national study found an increased risk of hospital admission or emergency care assistance for COVID-19 patients infected with the delta compared to the alpha. The results suggest that outbreaks of the delta variant in unvaccinated populations may result in a greater workload for hospital care than the alpha variant.

Evidence from this study in Scotland and England suggests that COVID-19 patients who are infected with the delta variant have approximately twice the risk of hospital admission  compared to patients with the alpha. This outcome should be taken into account for resource and policy planning in hospital care, particularly in areas where the delta variant is increasing and is likely to become the dominant circulating variant of SARS-CoV-2.

References delta variant study

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