The SARS-CoV-2 Delta (B1617.2) variant poses twice the risk of COVID-19 hospitalization as the Alpha (B117) strain, according to a large study late last week in The Lancet Infectious Diseases.
The study, led by researchers at Public Health England, is the first to report the hospitalization risks of the Delta and Alpha variants and the largest whole-genome SARS-CoV-2 sequencing effort in a high-income country, the authors said. It involved 43,338 English COVID-19 patients of all ages infected with either variant from Mar 29 to May 23, 2021.
Of all patients, 8,682 (20%) were infected with the Delta variant, with the remainder infected with the Alpha strain. The median age of Alpha patients was 31 years, compared with 29 years in those infected with Delta. Relative to Alpha patients, a higher proportion of Delta patients were Asian.
Delta became the dominant variant in England starting the week of May 17 (3,973 of 6,090 cases [65%]).
1.5 times the risk of emergency care
A total of 196 (2.3%) patients with the Delta variant and 764 (2.2%) with Alpha were hospitalized within 14 days of COVID-19 testing (adjusted hazard ratio [aHR], 2.26; 95% confidence interval [CI], 1.32 to 3.89).
The chances of either hospitalization or emergency care within 14 days were 1.5 times higher in those infected with Delta. Of all patients, 498 (5.7%) with Delta and 1,448 (4.2%) with Alpha were either hospitalized or sought emergency care (aHR, 1.45 [95% CI, 1.08 to 1.95]).
About three fourths of patients (32,078) were unvaccinated in both groups, with only 1.8% having received two doses, 24% having received one dose, and 74% unvaccinated (at the time, only high-risk UK residents were offered vaccines).
The aHRs for hospitalization or emergency care among vaccinated patients with the Delta versus the Alpha variant (1.94 [95% CI, 0.47 to 8.05]; 1.58 [95% CI, 0.69 to 3.61]) were similar to those of the unvaccinated (2.32 [95% CI, 1.29 to 4.16]; 1.43 [95% CI, 1.04 to 1.97]; P = 0·82 for both). However, precision was low for the vaccinated group because so few vaccinated patients were hospitalized.
"We already know that vaccination offers excellent protection against Delta, and, as this variant accounts for over 98% of COVID-19 cases in the UK, it is vital that those who have not received two doses of vaccine do so as soon as possible," coauthor Gavin Dabrera, MBBS, said in a Lancet news release.
Added burden on healthcare systems
Research is needed into severe COVID-19 outcomes such as length of hospitalization, admission to intensive care units, and other indicators of serious illness in patients with Delta or Alpha infections, the researchers said.
"Further work is also needed to measure the risk of mortality due to the delta variant, as a large proportion of the cohort included in this study was still within the 28-day follow-up period when analysis was done," they wrote.
In a commentary in the same journal, Jerome Lechien, MD, PhD, of Paris Saclay University, and Sven Saussez, MD, PhD, of CHU Saint-Pierre in Brussels, called for research into the risk of hospitalization and death by lineage after vaccination, the mechanisms of possible immune evasion, the function of the number of vaccine doses against Delta and Alpha, and the role of individual genetic differences in COVID-19 development.
But the most important study result is that outbreaks of the Delta variant in the unvaccinated could burden healthcare systems more than the Alpha strain, Lechien and Saussez said. "This information is important for future decision making, providing additional arguments to strengthen vaccination programmes worldwide before the spread of a new variant with resistance to the vaccines," they wrote.
