Retrospective methodology to estimate daily infections from deaths (REMEDID) in COVID-19: the Spain case study

Abstract

The number of new daily infections is one of the main parameters to understand the dynamics of an epidemic. During the COVID-19 pandemic in 2020, however, such information has been underestimated. Here, we propose a retrospective methodology to estimate daily infections from daily deaths, because those are usually more accurately documented. Given the incubation period, the time from illness onset to death, and the case fatality ratio, the date of death can be estimated from the date of infection. We apply this idea conversely to estimate infections from deaths. This methodology is applied to Spain and its 19 administrative regions. Our results showed that probable daily infections during the first wave were between 35 and 42 times more than those officially documented on 14 March, when the national government decreed a national lockdown and 9 times more than those documented by the updated version of the official data. The national lockdown had a strong effect on the growth rate of virus transmission, which began to decrease immediately. Finally, the first inferred infection in Spain is about 43 days before the official data were available during the first wave. The current official data show delays of 15–30 days in the first infection relative to the inferred infections in 63% of the regions. In summary, we propose a methodology that allows reinterpretation of official daily infections, improving data accuracy in infection magnitude and dates because it assimilates valuable information from the National Seroprevalence Studies.

Estimated number of deaths directly averted in people 60 years and older as a result of COVID-19 vaccination in the WHO European Region, December 2020 to November 2021

“…Here, w represents the time delays of 2 and 1 weeks for the development of a full immune response after, respectively, the first and second vaccine dose [ 14 ] and the median time from infection to death of 2 weeks [ 15 , 16 ]. The number of deaths averted each week was then added to the number of observed deaths to calculate the total expected number of deaths and cumulative mortality rate per 100,000 population per country.…”

Unequal impact of the Covid-19 pandemic on excess deaths, life expectancy, and premature mortality across Spanish regions in 2020 and 2021

“…Castile and León (244) whereas the Canary Island had the lowest rate (43). Finally, the European Committee on the Regions in a report of excess deaths in 2020 compared with the average number of deaths between 2016 and 2019, showed that Madrid was the hardest hit region in Europe, 44%, followed by Lombardia, Italy, 39%, and Castile La Mancha, 34%.…”

“…Madrid and its two nearby areas of influence, Castile-La Mancha, and Castile and León, had the highest excess mortality (48%, 74% and 80%, respectively) and the Canary Islands and other eight regions had lower deaths than expected. [42] Moreover, García-García et al [43] published a paper reporting excess deaths in Spain from 3 March to 29 November 2020 using the Mortality Monitoring (MoMo) surveillance system, designed to assess peaks when observed deaths from any cause are higher than those expected-as the average of the last 10 years-for at least two consecutive days. [44] Crude excess death rates per 100,000 population were higher in Castile La Mancha (347), Madrid (261), and…”

Caveats on COVID-19 herd immunity threshold: the Spain case

“…Three COVID-19 daily infection datasets for Spain were used, from 1 January to 29 November 2020: (1) official infections published by the Instituto de Salud Carlos III (ISCIII, 22 ); and Infections estimated with the REMEDID algorithm 23 from (2) official COVID-19 deaths 22 , and (3) excess of all-causes deaths (ED) from European Mortality Monitoring surveillance system (MoMo, 24 ). The REMEDID-derived infection data are more realistic than official infection data since they assimilate seroprevalence studies data 25 and known dynamics of COVID-19 (see 23 , for further discussion). As the last national longitudinal seroprevalence study in Spain finished on 29 November 2021, our REMEDID time series has been estimated up to that date.…”