Covid-19: Relative risks of non-vaccinated to vaccinated individuals

Abstract ObjectivesThe aim of this study was to evaluate and quantify the relative risk of hospital admission and death because of Sars-Cov2 infection between non-vaccinated and vaccinated individuals in Italy.MethodsData about vaccinated and non-vaccinated people, infections, hospital admissions, intensive care units and fatalities were extracted from the bulletin published by the Italian National Health Institute (Istituto Superiore di Sanità) on the 24th of December 2021. Likelihood ratios of hospital admission, intensive care and death were calculated between non-vaccinated and vaccinated people for each of the observed patient outcomes, in order to quantify the relative risk in the two sub-populations.ResultsNon-vaccinated people had a 3.1 time higher risk of becoming infected compared to vaccinated individuals. Non-vaccinated individuals had a 5.1 times higher risk of being admitted to hospital and a 10.4 times higher risk of becoming critical compared to vaccinated individuals. Further, non-vaccinated people had a 4.3 times higher risk to die compared to vaccinated individuals.ConclusionsThe relative risk of infection, hospital and intensive care admission is progressively higher in non-vaccinated compared to vaccinated individuals in case of infection by Sars-Cov2, as the condition worsens. Still, the relative risk does not increase further when the outcome is death, possibly because non-vaccinated individuals are younger and healthier of those who decided to take the vaccine. Individual conditions may play a more relevant role than the vaccine when the illness becomes critical.