COVID-19 Epidemiology during Delta Variant Dominance Period in 45 High-Income Countries, 2020-2021

Emerg Infect Dis. 2023 Sep;29(9):1757-1764. doi: 10.3201/eid2909.230142. Epub 2023 Jul 26.


The SARS-CoV-2 Delta variant, first identified in October 2020, quickly became the dominant variant worldwide. We used publicly available data to explore the relationship between illness and death (peak case rates, death rates, case-fatality rates) and selected predictors (percentage vaccinated, percentage of the population >65 years, population density, testing volume, index of mitigation policies) in 45 high-income countries during the Delta wave using rank-order correlation and ordinal regression. During the Delta-dominant period, most countries reported higher peak case rates (57%) and lower peak case-fatality rates (98%). Higher vaccination coverage was protective against peak case rates (odds ratio 0.95, 95% CI 0.91-0.99) and against peak death rates (odds ratio 0.96, 95% CI 0.91-0.99). Vaccination coverage was vital to preventing infection and death from COVID-19 during the Delta wave. As new variants emerge, public health authorities should encourage the uptake of COVID-19 vaccination and boosters.

Keywords: COVID-19; COVID-19 testing; SARS-CoV-2; coronavirus disease; demographic factors; epidemiology; morbidity; mortality; population density; primary prevention; respiratory infections; severe acute respiratory syndrome coronavirus 2; vaccination coverage; viruses; zoonoses.

MeSH terms

  • COVID-19 Vaccines
  • COVID-19* / epidemiology
  • COVID-19* / prevention & control
  • Developed Countries
  • Humans
  • SARS-CoV-2 / genetics


  • COVID-19 Vaccines

Supplementary concepts

  • SARS-CoV-2 variants