Does Delta increase the risk of hospitalization compared with Alpha?

Several variants of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which is the causative virus of the coronavirus disease 2019 (COVID-19), have been identified globally. Some of these variants have been described as variants of concern (VoC), which is a term that describes SARS-CoV-2 variants associated with developed transmissibility, enhanced infection severity or variation in clinical condition, and/or reduced effectiveness of public health and social standards or possible diagnostics, vaccines, and therapeutics.

Recently, a team of researchers from Norway conducted a cohort study to understand the risk of hospitalization in patients with either the Delta or Alpha variants of SARS-CoV-2. In their study, which is published on the preprint server bioRxiv*, the authors also estimated the vaccination efficacy in combating both variants.

Study: No difference in risk of hospitalization between reported cases of the SARS-CoV-2 Delta Variant and the Alpha variant in Norway. Image Credit: shutter_o /

About the study

The team conducted a cohort study on laboratory-confirmed cases of COVID-19 in Norway that were diagnosed between May 3, 2021, and August 15, 2021. The risk ratios were calculated and adjusted with 95% confidence intervals (CIs) using multivariable binomial regression. This accounted for variants, vaccination status, demographic characteristics, week of sampling, and underlying comorbidities.

Study findings

In the current study, 7,977 COVID-19 cases were found to be due to the Delta variant, whereas 12,078 of cases were due to the Alpha variant. Taken together, 347 (1.7%) of these cases were required hospitalization. The adjusted risk ratio of hospitalization for the Delta variant as opposed to the Alpha variant was 0.97.

Moreover, partially vaccinated patients had a 72% reduced risk of hospitalization, with fully vaccinated patients having a 76% reduced risk, in contrast to unvaccinated patients. The graph below illustrates the proportion of SARS-CoV-2 cases and the proportion of cases due to the Alpha and Delta variants.

The current study highlights the importance of considering the local epidemiological characteristics into account when trying to analyze the effect that various variants have on the COVID-19 epidemic in multiple settings. These results are illustrative of a growing cohort of COVID-19 cases in a country in which the health system managed well within potential, and where there was powerful vaccination coverage amongst people who were at greater risk of severe COVID-19. Vaccination coverage was also steadily increasing in Norway as Delta superseded the Alpha variant as the dominant variant.

The findings from this cohort study show no difference in the risk of hospitalization for individuals who were infected with the Delta variant as compared to the Alpha variant in Norway. Although these findings are promising, the scientists emphasize that more research from a broad variety of environments is needed to fully understand the relationship between the Delta variant and severe disease.

Data on the protection offered against severe disease are crucial to supervise future vaccination strategies. However, the results from this study and others indicate that partially and fully vaccinated persons are highly protected against hospitalization with COVID-19.

*Important notice

bioRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Journal reference:
Rashika Tripathi

Written by

Rashika Tripathi

Rashika Tripathi is a dental graduate from Bangalore, India. She first took an interest in medical communications when she started her health and lifestyle website. She went on to do various research in her field and worked as a research assistant. Thus, she grew in her profession, not just in clinical terms but also in the academic research base. Rashika worked as a freelance medical writer for various firms and hospitals and helped to expand their content.


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