There is insufficient clarity about the different outcomes between unvaccinated and vaccinated people hospitalized with Covid-19, with reference to the variables "Intensive Care Unit" and "Deaths". Moreover, it is unclear the real effectiveness of the vaccine boosters on the risks of infection and Covid-19 deaths, beyond the first few months after the booster. To verify the hypotheses that repeated vaccinations might expose to a progressively greater risk of severe Covid-19, and of a growing

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... kening of the immune response, primarily against infection, as the distance from the booster dose increases. Methods: Through an analysis of the official Italian data we calculated significant differences, percentage variations and trends in the variables "Intensive Care Units" and "Deaths" in hospitalized patients among four groups with different vaccination status, and between the Unvaccinated and Vaccinated groups. Through analyses of the UK Security Agency data in the weekly COVID-19 vaccine surveillance reports we explored the vaccine effectiveness against SARS-CoV-2 infections and against COVID-19 deaths in relation to the time elapsed from the booster doses. Results: Repeated vaccinations seem to expose the recipients to a growing risk of severe Covid-19, and fewer vaccinations might be enough to protect persons at greater risk. The vaccine effectiveness against infection vanished and reversed in the medium term, and vaccinated persons with three doses become increasingly more infected versus unvaccinated persons. Conclusions: The starting hypotheses have been supported, together with the need to combine carefully rethought vaccination campaigns with the implementation of other strategies, with the achievement of