Global between-countries variance in SARS-CoV-2 mortality is driven by reported prevalence, age distribution, and case detection rate

  1. Haris Babačić
  2. Janne Lehtiö
  3. Maria Pernemalm

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Abstract

Objective

To explain the global between-countries variance in number of deaths per million citizens ( nD pm ) and case fatality rate ( CFR ) due to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection.

Design

Systematic analysis.

Data sources

Worldometer, European Centre for Disease Prevention and Control, United Nations

Main outcome measures

The explanators of nD pm and CFR were mathematically hypothesised and tested on publicly-available data from 88 countries with linear regression models on May 1 st 2020. The derived explanators – age-adjusted infection fatality rate ( IFR ad j ) and case detection rate ( CDR ) – were estimated for each country based on a SARS-CoV-2 model of China. The accuracy and agreement of the models with observed data was assessed with R 2 and Bland-Altman plots, respectively. Sensitivity analyses involved removal of outliers and testing the models at five retrospective and four prospective time points.

Results

Globally, IFR adj estimates varied between countries, ranging from below 0.2% in the youngest nations, to above 1.3% in Portugal, Greece, Italy, and Japan. The median estimated global CDR of SARS-CoV-2 infections on April 16 th 2020 was 12.9%, suggesting that most of the countries have a much higher number of cases than reported.

At least 93% and up to 99% of the variance in nD pm was explained by reported prevalence expressed as cases per million citizens ( nC pm ), IFR adj , and CDR. IFR ad j and CDR accounted for up to 97% of the variance in CFR , but this model was less reliable than the nD pm model, being sensitive to outliers ( R 2 as low as 67.5%).

Conclusions

The current differences in SARS-CoV-2 mortality between countries are driven mainly by reported prevalence of infections, age distribution, and CDR . The nD pm might be a more stable estimate than CFR in comparing mortality burden between countries.

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  1. ScreenIT

    SciScore for 10.1101/2020.05.28.20114934: (What is this?)

    Please note, not all rigor criteria are appropriate for all manuscripts.

    Table 1: Rigor

    Institutional Review Board Statementnot detected.
    Randomizationnot detected.
    Blindingnot detected.
    Power Analysisnot detected.
    Sex as a biological variablenot detected.

    Table 2: Resources

    Software and Algorithms
    SentencesResources
    From these equations, nDτj is implied to have an inverse relation with the CDRi and will depend on the cumulative number of cases 14 days before the nDτj have occurred, and the age-adjusted IFRi:

    Assuming that the number of cases at the time of nDτj (nCτj) will have a constant dependence on the nCτi, as observed repeatedly in epidemics, including SARS-CoV-2, nCτj can replace it in the equation.

    SARS-CoV-2
    suggested: (Active Motif Cat# 91351, RRID:AB_2847848)

    Results from OddPub: Thank you for sharing your code and data.

    Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:
    Strengths and limitations: These models use very few explanators while maintaining high accuracy in explaining mortality. The sensitivity analyses demonstrated the robustness of the mathematical models when tested on real data. There is a remaining small proportion of variance than cannot be explained by the models, and this can be due to data mishandling or estimation errors, which limit the study. Independent of these limitations, the nDpm model remained robust. The CFR model was more sensitive to outliers than the nDpm model, and might be a less stable mortality outcome to follow SARS-CoV-2 mortality burden over time and across countries. The models were somewhat less accurate at earlier stages, which can be due to the amount of data (number of countries) used to build the models. Conclusions and policy implications: Overall, this study demonstrates that most countries are on a similar SARS-CoV-2 mortality trajectory as the number of cases increases, after adjusting for age distribution and CDR. These models should be used for less biased comparisons of mortality between countries. The nDpm model appears as a more stable indicator of SARS-CoV-2 infection mortality burden and should be favoured in following and comparing mortality within and between countries. Evidence before this study: -Verity and colleagues (Lancet Inf Dis 2020) have estimated the SARS-CoV-2 infection fatality rates (IFR) per age groups, and Vollmer & Bommer (2020) have estimated that the average case de...

    Results from TrialIdentifier: No clinical trial numbers were referenced.

    Results from Barzooka: We did not find any issues relating to the usage of bar graphs.

    Results from JetFighter: We did not find any issues relating to colormaps.

    Results from rtransparent:
    • Thank you for including a conflict of interest statement. Authors are encouraged to include this statement when submitting to a journal.
    • Thank you for including a funding statement. Authors are encouraged to include this statement when submitting to a journal.
    • No protocol registration statement was detected.

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  2. Version published to 10.1101/2020.05.28.20114934v1 on medRxiv