COVID-19 patients infected with the Delta variant (B.1.617.2) were more likely to need a higher level of care compared with those with the Alpha variant (B.1.1.7), British researchers found.
Patients infected with Delta were more than twice as likely to be admitted to the hospital within 14 days after PCR testing versus those with the Alpha variant (adjusted HR 2.26, 95% CI 1.32-3.89), reported Katherine Twohig, MPH, of Public Health England in London, and colleagues.
Delta variant patients were also more likely to seek emergency care or be hospitalized within 14 days versus Alpha variant patients (adjusted HR 1.45, 95% CI 1.08-1.95), the authors wrote in Lancet Infectious Diseases.
“To our knowledge, [this] is the largest study to date to report on [hospitalization] risk for the Delta variant compared with the Alpha variant, and the first to do so based on sequencing-confirmed variants,” they noted, adding that it may also be the first study to estimate risks for hospitalization or emergency care within the first 14 days.
Co-author Gavin Dabrera, MD, also of Public Health England, said that most of the patients in the analysis were unvaccinated and that the study “confirms previous findings that people infected with Delta are significantly more likely to require [hospitalization] than those with Alpha.”
Twohig and colleagues examined individual-level data on 43,338 patients who tested positive for COVID-19 from March 29 to May 23, 2021. Variants were identified through genomic sequencing. Overall, there were 34,656 cases of the Alpha variant and 8,682 cases of the Delta variant. Median patient age was 31, though patients with the Delta variant were younger (median age 29). About 70% of patients were white, and 51% were men.
Of the two variant groups, about 2% each were hospitalized within 14 days; 5.7% of patients with the Delta variant sought emergency care or were hospitalized within 14 days compared with 4.2% of patients with the Alpha variant.
Notably, almost three-quarters of patients were unvaccinated or were fewer than 21 days since their first dose of vaccine. Among vaccinated individuals, the risk for hospitalization (adjusted HR 1.94, 95% CI 0.47-8.05) and seeking emergency care or hospitalization (adjusted HR 1.58, 95% CI 0.69-3.61) were both non-significant when comparing the Delta variant with the Alpha variant. Among unvaccinated individuals, risk for hospitalization was higher (adjusted HR 2.32, 95% CI 1.29-4.16), as was risk for hospitalization or seeking emergency care (adjusted HR 1.43, 95% CI 1.04-1.97) for Delta versus Alpha.
However, the differences between vaccinated and unvaccinated groups for hospitalization and emergency care or hospitalization were non-significant (P=0.82 for both). “The precision for the vaccinated subgroup was low,” noted the authors.
Limitations to the data included residual confounding and misclassification resulting in the potential inclusion of non-COVID-related visits. In addition, there were no available data on comorbidities, the authors said.
This study was supported by the Medical Research Council, U.K. Research and Innovation, the Department of Health and Social Care, and the National Institute for Health Research.
Twohig disclosed no conflicts of interest.
Dabrera’s employer, Public Health England, received funding from GlaxoSmithKline for a research project related to seasonal influenza and antiviral treatment; this project preceded and had no relation to COVID-19.