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Objective To assess the evolution of COVID-19 severity and fatality in a unique setting that consistently applied, throughout the pandemic, rigorous and standardised criteria for defining severe COVID-19 outcomes.Methods and analysis We conducted a national cohort study on 312 109 Qatari citizens to investigate incidence of severe, critical or fatal COVID-19 classified according to the WHO criteria between 28 February 2020 and 21 April 2023. Incidence rates for severe, critical or fatal COVID-19 were estimated during the pre-omicron phase, first omicron wave, combined phases and throughout the pandemic.Results Cumulative incidence of severe, critical or fatal COVID-19 after 3.14 years of follow-up was 0.45% (95% CI 0.43% to 0.47%). Incidence rate for severe, critical or fatal COVID-19 throughout the pandemic was 1.43 (95% CI 1.35 to 1.50) per 1000 person years. In the pre-omicron phase, first omicron wave, and combined phases, it was 2.01 (95% CI 1.90 to 2.13), 3.70 (95% CI 3.25 to 4.22) and 2.18 (95% CI 2.07 to 2.30) per 1000 person years, respectively. The post-first omicron phase saw a drastic drop to 0.10 (95% CI 0.08 to 0.14) per 1000 person years, a 95.4% reduction. Among all severe, critical and fatal cases, 99.5% occurred during the primary infection. Cumulative incidence of fatal COVID-19 was 0.042% (95% CI 0.036% to 0.050%), with an incidence rate of 0.13 (95% CI 0.11 to 0.16) per 1000 person years. In the post-first omicron phase, incidence rate of fatal COVID-19 decreased by 90.0% compared with earlier stages. Both severity and fatality exhibited an exponential increase with age and a linear increase with the number of coexisting conditions.Conclusion The conclusion of the first omicron wave was a turning point in the severity of the pandemic. While vaccination and enhanced case management reduced severity gradually, the rapid accumulation of natural immunity during the first omicron wave appears to have played a critical role in driving this shift in severity.

Objective To investigate all-cause mortality, COVID-19 mortality and all-cause non-COVID-19 mortality in Qatar during the COVID-19 pandemic.Methods A national, retrospective cohort analysis and national, matched, retrospective cohort studies were conducted between 5 February 2020 and 19 September 2022.Results There were 5025 deaths during a follow-up time of 5 247 220 person-years, of which 675 were COVID-19 related. Incidence rates were 0.96 (95% CI 0.93 to 0.98) per 1000 person-years for all-cause mortality, 0.13 (95% CI 0.12 to 0.14) per 1000 person-years for COVID-19 mortality and 0.83 (95% CI 0.80 to 0.85) per 1000 person-years for all-cause non-COVID-19 mortality. Adjusted HR, comparing all-cause non-COVID-19 mortality relative to Qataris, was lowest for Indians at 0.38 (95% CI 0.32 to 0.44), highest for Filipinos at 0.56 (95% CI 0.45 to 0.69) and was 0.51 (95% CI 0.45 to 0.58) for craft and manual workers (CMWs). Adjusted HR, comparing COVID-19 mortality relative to Qataris, was lowest for Indians at 1.54 (95% CI 0.97 to 2.44), highest for Nepalese at 5.34 (95% CI 1.56 to 18.34) and was 1.86 (95% CI 1.32 to 2.60) for CMWs. Incidence rate of all-cause mortality for each nationality group was lower than the crude death rate in the country of origin.Conclusions Risk of non-COVID-19 death was low and was lowest among CMWs, perhaps reflecting the healthy worker effect. Risk of COVID-19 death was also low, but was highest among CMWs, largely reflecting higher exposure during first epidemic wave, before advent of effective COVID-19 treatments and vaccines.

Objective To define the epidemiological curve of COVID-19 in Qatar and determine factors associated with severe or critical illness.Design Case series of first 5685 COVID-19 cases in Qatar.Setting and participants All confirmed COVID-19 cases in the State of Qatar between 28 February and 18 April 2020.Main outcome measures Number of total and daily new COVID-19 infections; demographic characteristics and comorbidity burden and severity of infection; factors associated with severe or critical illness.Results Between 28 February and 18 April 2020, 5685 cases of COVID-19 were identified. Median age was 34 (IQR 28–43) years, 88.9% were male and 8.7% were Qatari nationals. Overall, 83.6% had no concomitant comorbidity, and 3.0% had three or more comorbidities. The overwhelming majority (90.9%) were asymptomatic or with minimal symptoms, with 2.0% having severe or critical illness. Seven deaths were observed during the time interval studied. Presence of hypertension or diabetes was associated with a higher risk of severe or critical illness, but age was not. The epidemiological curve indicated two distinct patterns of infection, a larger cluster among expatriate craft and manual workers and a smaller one among Qatari nationals returning from abroad during the epidemic.Conclusion COVID-19 infections in Qatar started in two distinct clusters, but then became more widespread in the population through community transmission. Infections were mostly asymptomatic or with minimal symptoms and associated with very low mortality. Severe/critical illness was associated with presence of hypertension or diabetes but not with increasing age.