In a recent study published in the International Journal of Epidemiology, researchers presented a comprehensive approach to estimating long coronavirus disease (COVID)-associated morbidity in the Australian population.
The approach analyzed the period during severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Omicron variant of concern (VOC) dominance between 2021 and 2022.
Study: The health impact of long COVID during the 2021–2022 Omicron wave in Australia: a quantitative burden of disease study. Image Credit: tilialucida/Shutterstock.com
Background
Post-COVID-19 condition (PCC) or long COVID symptoms occur among a considerable proportion of individuals following acute COVID 2019 (COVID-19), less frequently among vaccinated individuals in the post-acute phase of Omicron VOC infections than Delta VOC infections.
Given the continual rise in SARS-CoV-2 transmission across the globe, it is critical to assess the burden of COVID-19 quantitatively and the associated long-term consequences.
Prior pre-Omicron VOC-associated PCC estimates were reported, analyzing only main symptoms, lacking adequate control groups, and therefore, not acknowledging the true extent of and heterogeneity in PCC symptomatology.
The scarcity of high-quality data on PCC symptoms precludes quantifying the global PCC burden is clear. Moreover, most long COVID studies comprised unvaccinated individuals infected in the pre-Omicron VOC period.
About the study
In the present study, researchers provided comprehensive estimates of long COVID-associated morbidity, analyzing individual PCC symptoms experienced during Omicron dominance in Australia.
To precisely quantify PCC effects among COVID-19 vaccinees during Omicron predominance, differences in PCC risks by COVID-19 vaccination status and SARS-CoV-2 VOC were assessed.
PCC-associated morbidity, resulting from Omicron infections, was estimated, assessing the onset, severity, and duration of every PCC symptom. PCC-related years lived with disability (YLDs) during Omicron BA.1, and BA.2 predominance was calculated by evaluating previous cross-sectional, cohort-based, and case-control studies' data, determining the duration and prevalence of each PCC symptom.
The predicted health losses were compared to that associated with acute COVID-19-associated years lived with disability and the years of life lost (YLLs) due to SARS-CoV-2 infections.
Totaling the components yielded COVID-19-associated disability-adjusted life years (DALYs), compared to DALYs associated with other diseases reported in the global burden of disease (GBD) study 2019.
The team quantified long COVID symptom severity as disability weights (DW), reported in the global burden of disease study. Base case prevalence estimates for unvaccinated and pre-Omicron VOC-infected individuals were multiplied by an odds ratio (OR) of 0.6 to evaluate long COVID symptom prevalence among COVID-19 vaccinees.
Prevalence estimates were multiplied by OR 0.3, based on an estimate of reductions in the prevalence of any long COVID symptom ≥4.0 weeks post-Omicron VOC infection than Delta VOC infection among COVID-19 vaccinees residing in the United Kingdom.
PCC YLDs were calculated as the estimated PCC-associated morbidity for every symptomatic infection, multiplied by the number of symptomatic BA.1 and BA.2 infections between December 10, 2021, and April 9, 2022.
Data on the national-level COVID-19 vaccinations and symptom duration for hospitalized patients were obtained from a New South Wales (NSW)-based study.
The team performed sensitivity analyses by varying prevalence rates of physical, cognitive, and psychological symptoms. Further, an extreme case scenario was analyzed by applying the odds ratio for SARS-CoV-2 Omicron VOC vs. pre-Omicron VOC infections (OR 0.3) to hospitalized patients.
Results
In Australia, five million SARS-CoV-2 infections were documented during the initial four months of Omicron predominance, with 35,500 and 3,463 hospital admissions and deaths, respectively, and predicted 61% of the infected individuals were COVID-19 vaccinees.
In total, 5,200 YLDs and 1,800 YLDs were attributed to PCC, and acute COVID-19, respectively, indicating that PCC caused 74.0% of the COVID-19-associated YLDs during BA.1 and BA.2 predominance.
50,900 DALYs were attributed to SARS-CoV-2, representing two percent of expected DALYs for all diseases in the period, and PCC contributed 10%. This was compared with 3.6% DALYs resulting from acute SARS-CoV-2 infection-associated morbidity and the remaining DALYs from acute SARS-CoV-2 infection-associated mortality.
The team obtained most PCC YLDs from cases in community settings, of which the majority were observed among vaccinated adults (2,200 YLDs), given that the group represented 51% of the documented long COVID cases.
COVID-19-associated morbidity showed a comparable extent of non-lethal health losses associated with chronic renal disorders and myocardial ischemia. COVID-19 was listed in Australia's top ten reasons for DALYs during the study period. For adult COVID-19 vaccinees with no hospitalization needs during acute COVID-19, 0.10% of a healthy year of life was estimated as lost due to PCC (or 33% of one day of healthy life lost).
Sensitivity analyses decreased overall PCC morbidity by 12.0% compared to the prime analysis, to 4,600 YLDs. The estimated PCC morbidity was within 20% of the Institute for Health Metrics and Evaluation (IHME) estimate, indicating that the present study approach was valid.
Conclusions
Overall, the study findings highlighted PCC effects among Australians, evaluated using the disease burden-type approach, providing a more accurate estimate of the PCC burden than that reported in prior studies.
PCC contributed to 74.0% of non-lethal loss of health, resulting from documented BA.1 and BA.2 infections in Australia. Increasing PCC symptom data would enhance the accuracy of the study findings.
Additionally, PCC symptom prevalence is lower for Omicron infections and among COVID-19 vaccinees than pre-Omicron infections among unvaccinated individuals.
However, PCC contributes to considerable loss of health regardless of vaccine protection when summing up the infection estimates. Thus, PCC must be considered while formulating COVID-19 mitigation policies and strategies.