Estimating the Percentage of a Population Infected with SARS-CoV-2 Using the Number of Reported Deaths: A Policy Planning Tool

Abstract

The magnitude of future waves of Covid19 in a population will depend, in part, on the percentage of that population already infected, recovered, and presumably immune. Sero-epidemiological surveys can define the prevalence of SARS-CoV-2 antibodies in various populations. However, sero-surveys are resource-intensive and methodologically challenging, limiting widespread use. We propose a relatively simple method for calculating the percentage of a population infected, which depends on the number of reported Covid19 deaths, a figure usually more reliable and less dependent on variable testing practices than the total number of reported Covid19 cases, and the infection fatality rate, a figure that is relatively stable in similar populations. The method can be applied in different sized areas, such as states, districts, or cities. Such an approach can provide useful, real-time estimates of probable population immunity in settings unable to undertake multiple sero-surveys. This method is applicable to low- and lower-middle-income country (LMIC) settings where sero-survey data will likely be limited; however, better estimates of infection fatality rates and Covid19 death counts in LMICs are needed to improve the method’s accuracy. Information on the percentage of a population infected will help public health authorities in planning for future waves of Covid19, including where to most effectively deploy vaccines.

Rapid evolution of SARS-CoV-2 challenges human defenses

“…The verified number of diagnosed COVID-19 infections is known to drastically underestimate real infections, and the ratio between the two varies greatly depending on time and geographic region 6 , 7 . Confirmed COVID deaths also underestimate real COVID deaths, but are much more accurate compared to confirmed infections 8 , 9 . We therefore adopted a model that combines the reported COVID-19 deaths 6 which is just over 4.8 million worldwide (by October 5, 2021), with an infection fatality ratio to calculate infections 9 .…”

“…Confirmed COVID deaths also underestimate real COVID deaths, but are much more accurate compared to confirmed infections 8 , 9 . We therefore adopted a model that combines the reported COVID-19 deaths 6 which is just over 4.8 million worldwide (by October 5, 2021), with an infection fatality ratio to calculate infections 9 . We improved this model to account for the demographics for each country along with age-specific infection fatality ratios 6 .…”

Understanding COVID-19 Epidemiology and Implications for Control: The Experience from a Greek Semi-Closed Community

“…Limiting the study to groups with high infection rates and risk of exposure can mitigate bias while improving power. Preliminary results from a serosurvey in Mumbai, India, showed 58% of slum-dwellers versus 17% of the non-slum population had antibodies to SARS-CoV-2 [24,26,27]. The semi-closed community of Deskati has among the highest SARS-CoV-2 seroprevalence rate described in the literature.…”

Epidemiological waves - types, drivers and modulators in the COVID-19 pandemic

“…Also, most countries have vastly increased their testing capacity over time, so that the case ascertainment rate is now far greater than that in place when restrictions were initially introduced [14]. This creates difficulty in deciding how serious the present situation is and how it compares with the first wave of transmission as well as in describing the spread of the epidemic to the public [20] and has inspired researchers to propose methods of using mortality data as a more reliable proxy for infection numbers [9,12,18].…”