Covid-19 vaccines work but other factors play a relevant role: a data analysis on spread and mortality in 24 countries.

Abstract

Background: The aim was to outline a methodology to monitor the impact of vaccinations in different countries comparing in two different time within countries and between countries the frequency of new cases and Covid-19 related deaths and the percentage of vaccinations conducted.Design and methods: The 25 countries with the largest increase in SARS-CoV-2 cases on 8 August 2021 were evaluated. In each nation was calculated the proportion of Covid-19 deaths divided per new cases x 100 and the proportion of new cases per 1.000 inhabitant on 10 January 2021 (before vaccinations’ distribution) and 8 August 2021 (when large percentage of the population had been vaccinated in many countries).Results: The study shows that in the countries with the highest number of cases as of 8 August 2021, the proportion of vaccinations carried out in the population correlates negatively with both the proportion between Covid-19 dead people x100 infected people and with the rate of new cases. However, the proportion of vaccinations does not correlate with the differences in the two same indicators considered in the weeks observed, thus additional factors seem to play an important role.Conclusions: This work indicates that mass vaccination is associated with a lower spread of the pandemic and, to greater extent, with a lowering of mortality in infected people. Significance for public health The Covid-19 pandemic has been effectively impacted by the development and dissemination of vaccines. Despite initial promising data subsequent publications suggest that all vaccines, including mRNA vaccines- appear to be less effective against the new variants of the virus but they continue to provide protection against the worst SARS-CoV-2 clinical outcomes and therefore strong effective lower mortality, with possible different efficacy for the different types of vaccines on different variants (e.g., Delta variant). A greater attention to epidemiological factors is needed to develop synergic strategies. Furthermore, there is a growing need to understand the impact and limitations of vaccination campaigns.