September 2021

Delta Hospitalization Risk Twice That of Alpha

A study published in The Lancet Infectious Diseases adds evidence to what many experts already suspected: people infected with the highly contagious SARS-CoV-2 Delta variant are twice as likely to be hospitalized as those infected with the Alpha variant. To compare hospitalization rates, researchers from Public Health England (PHE) and Cambridge University examined data on 43,338 sequencing-confirmed COVID-19 cases between March 29 and May 23, 2021, during which time the Delta variant was becoming the predominant variant in the UK. The majority of the cases were among unvaccinated individuals (74%), while 2% were fully vaccinated and 24% had received one dose. Of 34,656 Alpha cases, 764 (2.2%) were admitted to the hospital within 14 days of a positive SARS-CoV-2 test, while 196 of 8,682 (2.3%) Delta cases were hospitalized. Although the percentages of hospitalized cases were similar between both variants, the risk of being hospitalized more than doubled (adjusted hazard ratio [HR] 2.26, 95% confidence interval [CI] 1.32-3.89) for Delta cases compared with Alpha cases when the researchers adjusted the data to account for certain factors, including age and sex. Delta cases also were more likely to seek emergency medical care or be hospitalized within 14 days versus Alpha cases (adjusted HR 1.45, 95% CI 1.08-1.95).

In a statement, Dr. Anne Presanis, Senior Statistician at the University of Cambridge and a lead author of the study, emphasized the importance of getting fully vaccinated to reduce the risk of symptomatic infection with Delta, as well as reduce the risk of severe disease and hospitalization. The researchers noted that a previous study conducted in Scotland and published in June showed a similar increase in hospitalization risk among people infected with the Delta variant. While the UK study is the largest to date examining hospitalization risk for the Delta versus Alpha variants based on whole-genome sequenced cases, the researchers called for further assessments into how hospitalization risks differ for vaccinated individuals after infection with either variant.

— Johns Hopkins Bloomberg School of Public Health

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