Modeling the asymptomatic prevalence of SARS-CoV-2 epidemic in Italy and the ISTAT survey

Abstract

objectivesAugust 3rd, 2020, the Italian National Institute of Statistics (ISTAT) presented preliminary results of seroprevalence survey on the percentage of individuals affected by Covid-19. The survey aims to define (within the entire population of Italy) the portion of individuals that developed an antibody response against SARS-CoV-2. For the first time one has an estimate of the asymptomatic infected population and the possibility to acknowledge its potential rôle in the infection spread in Italy, one of the most affected areas in Europe. The information obtained allow a particularly sensitive validation of epidemiological models which include the asymptomatic class.methodsThe present study is devoted to the construction of a model able to simulate, in a systematic way, the asymptomatic group whose relevance in the, SARS-CoV-2 epidemic, has been recently investigated and discussed. The investigation involves the description of the first epidemic outbreak in Italy as well as the predictive analysis of the ongoing second wave. In particular the possible correction to the data of the serological tests because of their sensitivity and specificity.resultsThe model: taken as an example of the models presently used, satisfactory reproduces the data of the ISTAT survey showing a relevant predictive power and relegating in a secondary position models which do not include, in the simulation, the presence of asymptomatic groups. The corrections due to the serological test sensitivity (in particular those ones depending on the symptoms onset) make the comparison between data and models less accurate.conclusionsThe predictions of the model confirm a relevant presence of asymptomatic individuals also during the second pandemic wave in Italy. The ratio of reported to unreported cases is predicted to be roughly 1:4. A more detailed knowledge of the results of the survey could allow to correct, in a relevant way, the data by means of the experimental evidences on the antibodies sensibility. The model analyses of the vaccination strategies, confirms the relevance of a massive administration with the beginning of the year to arrive at the end of the infection within August 2021.

Modelling SARS-CoV-2 unreported cases in Italy: Analysis of serological survey and vaccination scenarios

“…The parametrization is based on values indicated in Table II of ref. (Traini, 2021a) ( Traini et al, 2021a ), no ad hoc modifications are introduced. The model, formulated in April 2020 (Traini, 2020) ( Traini et al, 2020 ) is simply normalized to the value of the reported cases of September 25th (47718), as indicated in the official site of the Ministry of Heath (Ministero della Salute) (Ministero della Salute, 2020) ( Ministerodella Salute, 2020 ).…”

“…Table II of ref. (Traini, 2021a) ( Traini et al, 2021a )); in a (large and representative) sample, the portion of individuals reached by the infection in the previous months is fixed (next discussion will be largely devoted to investigate this point). …”

“…Aim of the present paper is the study of the large unreported component, characterizing the SARS-CoV-2 epidemic event in Italy, taking advantage of the Istat survey ( IstatItalian National Institute of Statistics, 2020 ). The model used assumes eight compartments (groups) including symptomatic reported and unreported, quarantined, asymptomatic, threatened (hospitalized) and recovered, a model recently proposed to discuss the role of measures against the Italian outbreak (Traini, 2020; Traini 2021a) ( Traini et al, 2020 , 2021a ); a Markov-Chain-Monte-Carlo method is used to fix the parameters. The model has been first formulated for the Wuhan outbreak (Tang, 2020a) ( Tang, Wang, et al, 2020 ), (Tang, 2020b) ( Tang, Bragazzi, et al, 2020 ).…”