A scaling approach to estimate the age-dependent COVID-19 infection fatality ratio from incomplete data

Abstract

SARS-CoV-2 has disrupted the life of billions of people around the world since the first outbreak was officially declared in China at the beginning of 2020. Yet, important questions such as how deadly it is or its degree of spread within different countries remain unanswered. In this work, we exploit the ‘universal’ increase of the mortality rate with age observed in different countries since the beginning of their respective outbreaks, combined with the results of the antibody prevalence tests in the population of Spain, to unveil both unknowns. We test these results with an analogous antibody rate survey in the canton of Geneva, Switzerland, showing a good agreement. We also argue that the official number of deaths over 70 years old might be importantly underestimated in most of the countries, and we use the comparison between the official records with the number of deaths mentioning COVID-19 in the death certificates to quantify by how much. Using this information, we estimate the infection fatality ratio (IFR) for the different age segments and the fraction of the population infected in different countries assuming a uniform exposure to the virus in all age segments. We also give estimations for the non-uniform IFR using the sero-epidemiological results of Spain, showing a very similar increase of the fatality ratio with age. Only for Spain, we estimate the probability (if infected) of being identified as a case, being hospitalized or admitted in the intensive care units as function of age. In general, we observe a nearly exponential increase of the fatality ratio with age, which anticipates large differences in total IFR in countries with different demographic distributions, with numbers that range from 1.82% in Italy, to 0.62% in China or even 0.14% in middle Africa.

Overview of coronavirus pandemic

“…IFR increases by age, from 0.005% for children to 0.4% at age 55, 1.4% at age 65, and 15% for ages 85 and above. This upward trend in percentages can be found similarly with the CFR, from 1.3% at age 55, 3.6% at age 65, and 8% at age 70 ( Kavaliunas et al, 2020 , Levin et al, 2020 , Public Health Agency of Sweden, 2020 , Seoane and Tu, 2021 ).…”

“…Within the age ranges, men tend to have twice the risk than women (in the large Spanish seroprevalence study, 1.14% versus 0.58% values that are similar to other studies) ( Pastor-Barriuso et al, 2020 ). Some authors speculate that the higher mortality in men could result from more health comorbidities than in women, and also differences in cellular immunity between men and women (including poorer T cell activation and an increase in proinflammatory cytokines in men) ( Català et al, 2021 , Levin et al, 2020 , Seoane and Tu, 2021 ).…”

Analysis of the COVID-19 pandemic: lessons towards a more effective response to public health emergencies

“…Estimates of prevalence based on sero-surveys, which includes asymptomatic and mildly symptomatic infections, can be used to estimate IFR [93]. In a systematic review of 17 studies, seroprevalence rates ranged from 0.22% in Brazil to 53% in Argentina [94].…”

Temporal trends in hospitalizations and 30-day mortality in older patients during the COVID pandemic from March 2020 to July 2021

“…Age is among the strongest risk factors for COVID-19 and the infection fatality ratio after age 70 is substantial. 2, 3 Here, we present data on geriatric hospitalizations for COVID-19 and other causes, including 30-day mortality from admission and compare these to the incidence of COVID-19 and 30-day mortality from COVID-19 in the Stockholm region for persons 70+. We aim to describe how COVID-19 peaks affected geriatric patients 70 and older hospitalized both for COVID-19 and for other causes in Stockholm.…”