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Abstract

Background: To assess the comprehensive dynamics of outcomes during the SARS-CoV-2 B.1.617.2 (Delta variant) compared to the Alpha variant outbreak in the United Kingdom.

Methods: In this observational study of the cases reported by Public Health England for confirmed (sequencing and genotyping), SARS-CoV-2 cases Delta variant (n=592,692) and Alpha variant (n=150,934) were used. Outcomes were analyzed by age groups and compared with all reported weekly cases in the UK.

Results: The Delta variant surge is associated with a significantly lower case fatality rate (0.43% vs. 1.07; RR 0.39; 95% CI 0.37- 0.42; P<0.0001); lower odds of hospitalization (2.1% vs. 3.0%; RR 0.70; 95% CI 0.68-0.73; P<0.0001) than the Alpha variant. During the Delta variant surge there were significant increased cases (11.3% to 21.1%, RR 1.87; 95% CI 1.84-1.89; P<0.0001), hospitalizations (40.2% to 56.5%; RR 1.40, 95% CI 1.3-1.46; P<0.0001) among confirmed Delta variant cases in the ≥ 50 years age group during the August 3-September 12, 2021 period compared to earlier reported cases. There was also a significant increase in total weekly COVID-19 deaths noted among ≥ 70 years old age group (71.4% to 75.1%; RR 1.05; 95% CI 1.01-1.08; P=0.0028) during August 6-October 8, 2021 compared to June 4-July 30, 2021 period.

Conclusion: The Delta variant surge is associated with significantly lower mortality and hospitalizations than the Alpha variant. As the Delta variant surge progressed, ≥ 50 years old had a significant increased percentage of cases, hospitalizations and a significant increased COVID-19 deaths occurred among ≥ 70 years old age group.

Keywords: Changing dynamics; Delta variant; Alpha variant