Severity of Illness in Persons Infected With the SARS-CoV-2 Delta Variant vs Beta Variant in Qatar.

Importance: The Delta variant is now the predominant circulating SARS-CoV-2 strain worldwide. Severity of illness in persons infected with the SARS-CoV-2 Delta variant compared with the Beta variant is not known. Objective: To directly compare clinical outcomes in persons infected with the SARS-CoV-2 Delta variant vs those infected with the Beta variant in Qatar. Design, Setting, and Participants: This retrospective cohort study used data from the national COVID-19 database in Qatar, which includes information on all individuals who were ever tested for SARS-CoV-2 using a reverse transcriptase-polymerase chain reaction test and all individuals who received any SARS-CoV-2 vaccine in Qatar. Among persons with confirmed SARS-CoV-2 infection between March 22 and July 7, 2021, those infected with the Delta variant were identified and were propensity score matched with control individuals infected with the Beta variant. The variants were ascertained by variant genotyping of the positive samples. Exposures: SARS-CoV-2 infection with the Delta or Beta variant. Main Outcomes and Measures: The main outcomes were admission to the hospital, admission to the intensive care unit, use of supplemental oxygen, use of high-flow oxygen, receipt of mechanical ventilation, or death among those infected with the Delta or Beta variant overall and stratified by vaccination status. Results: Among 1427 persons infected with the Delta variant (252 [55.9%] male; median age, 34 years [IQR, 17-43 years]) and 5353 persons infected with the Beta variant (233 [51.7%] male; median age, 34 years [IQR, 17-45 years]), 451 propensity score-matched pairs were identified. Persons infected with the Delta variant were more likely to be hospitalized (27.3% [95% CI, 23.2%-31.6%] vs 20.0% [95% CI, 16.4-24.0]; P = .01) or to have mild-moderate or severe-critical disease outcomes (27.9% [95% CI, 23.8%-32.3%] vs 20.2% [95% CI, 16.6%-24.2%]; P = .01) compared with persons infected with the Beta variant. Infection with the Delta variant was independently associated with higher odds of experiencing any adverse outcome (adjusted odds ratio [aOR], 2.53; 95% CI, 1.72-3.72). Compared with being unvaccinated, being vaccinated with a second dose more than 3 months before infection was associated with lower odds of any adverse outcome among persons infected with the Delta variant (aOR, 0.11; 95% CI, 0.04-0.26) and among those infected with the Beta variant (aOR, 0.22; 95% CI, 0.05-0.98). Protection was similar among those who received a second vaccine dose less than 3 months before infection, but having received only a single dose was not associated with a lower odds of any severe outcome among those infected with the Delta variant (aOR, 1.12; 95% CI, 0.41-3.06) or those infected with the Beta variant (aOR, 0.74; 95% CI, 0.20-2.72). Conclusions and Relevance: In this cohort study of persons with COVID-19 in Qatar, infection with the SARS-CoV-2 Delta variant was associated with more severe disease than was infection with the Beta variant. Being unvaccinated was associated with greater odds of severe-critical disease.