On 7 June 2021, researchers at the National Centre for Infectious Diseases in Singapore posted a paper suggesting that patients testing positive for Delta are more likely to develop pneumonia and/or require oxygen than patients with wild type or Alpha.
On June 14, researchers from Public Health Scotland found that the risk of hospitalization from Delta was roughly double that of from Alpha.
On June 11, Public Health England released a report finding that there was "significantly increased risk of hospitalization" from Delta as compared with Alpha.
On July 9, Public Health England reported that the Delta variant in England had a case fatality rate (CFR) of 0.2%, while the Alpha variant's case fatality rate was 1.9%, although the report warns that "case fatality rates are not comparable across variants as they have peaked at different points in the pandemic, and so vary in background hospital pressure, vaccination availability and rates and case profiles, treatment options, and impact of reporting delay, among other factors. " James McCreadie, a spokesperson for Public Health England, clarified "It is too early to assess the case fatality ratio compared to other variants."
On 12 July, a preprint study from epidemiologists at the University of Toronto, Canada found that Delta had a 120% greater risk of hospitalization, 287% greater risk of ICU admission and 137% greater risk of death compared to non-variant of concern strains of SARS-COV-2.88