Publication date: 02/10/2023 – E&P Code: repo.epiprev.it/2824
Authors: Giovanni Malatesta1, Alberto Donzelli2, Marco Alessandria3, Franco Berrino4
Abstract: The SARS-CoV-2 pandemic has led to an unprecedented effort to generate real evidence on the safety and effectiveness of various treatments, mRNA vaccines included. We can now welcome with great interest the publication of a new article on mortality in the general population of the Italian province of Pescara, divided by vaccination status, with a follow-up of two years (1).
Already in articles published during the pandemic (2, 3) it has been argued that, in observational cohort studies, an incorrect management of follow-up times may introduce the so-called Immortal-Time Bias (ITB) in favour of the exposed group. Nevertheless, ITB still appears to be present in several cohort studies. As highlighted in an article (Intervention) recently published in Epidemiologia&Prevenzione (4), a study on the safety of COVID-19 vaccines in the population of an Italian province is no exception (5). A possible explanation that the ITB is still largely prevalent in such cohort studies may be that the structure of the ITB is still poorly understood (3). A new study on the effectiveness of COVID-19 vaccines (1) in the same Italian province as that examined in the article (5) we have previously considered (4) repeats the aforementioned bias, along with others, similarly common, that we have discussed before.
Errata corrige: nel grafico a pagina 3 la cifra 1,896,676 è stata coretta in 186,676 (11 ottobre 2023)