A Bayesian estimate of the early COVID-19 infection fatality ratio in Brazil based on a random seroprevalence survey

Valerio Marra,Miguel Quartin

doi:10.1016/j.ijid.2021.08.016

Abstract

Background:A number of estimates of the infection fatality ratio (IFR) of SARS-CoV-2 in different countries have been published. In Brazil, the fragile political situation, together with socioeconomic and ethnic diversity, could result in substantially different IFR estimates.Methods:We infer the IFR in Brazil in 2020 by combining three datasets. We compute the prevalence via the population-based seroprevalence survey, EPICOVID19-BR. For the fatalities we obtain the absolute number using the public Painel Coronavírus dataset and the age-relative number using the public SIVEP-Gripe dataset. The time delay between the development of antibodies and subsequent fatality is estimated via the SIVEP-Gripe dataset. We obtain the IFR for each survey stage and 27 federal states. We include the effect of fading IgG antibody levels by marginalizing over the test detectability time window.Results:We infer a country-wide average IFR (maximum posterior and 95% CI) of 1.03% (0.88–1.22%) and age-specific IFRs of 0.032% (0.023–0.041%) [< 30 years], 0.22% (0.18–0.27%) [30–49 years], 1.2% (1.0–1.5%) [50–69 years], and 3.0% (2.4–3.9%) [≥ 70 years]. We find that the fatality ratio in the country increased significantly at the end of June 2020, likely due to the increased strain on the health system.Conclusions: Our IFR estimate is based on data and does not rely on extrapolating models. This estimate sets a baseline value with which future medications and treatment protocols may be confronted.

Highlights

The infection fatality ratio (IFR) – the ratio between the number of deaths from a disease and the number of infected individuals – is one of the most important quantities of any new disease
This forward 20-day window makes Painel Coronavírus consistent with SIVEP-Gripe during the first months of the pandemic, when one expects that deaths at hospitals, tracked by SIVEP-Gripe, dominate the overall count
For T > 80 days, the results converge and the IFR remains unchanged. This is due to the fact that the present analysis addresses the early stages of the pandemic in Brazil (May and June 2020) and there were no deaths before March 2020

Summary

Introduction

The infection fatality ratio (IFR) – the ratio between the number of deaths from a disease and the number of infected individuals (irrespective of developing symptoms) – is one of the most important quantities of any new disease. In order to estimate the IFR, one needs an estimate of the number of deaths and of the total infected population, and to compare both within the same time period. It is, The total number of deaths during an epidemic can be biased by the mislabeling of undiagnosed fatalities. In the case of COVID-19 this method is being pursued by many groups [2,43,45], including the mainstream media, as a method which is complementary to the officially reported numbers This approach invariably suffers from important modeling uncertainties [45]. In Brazil, the fragile political situation, together with socioeconomic and ethnic diversity, could result in substantially different IFR estimates

Methods

Results

Conclusion