Vaccination against seasonal influenza and socio-economic and environmental factors as determinants of the geographic variation of COVID-19 incidence and mortality in the Italian elderly

Background: A possible protective effect of seasonal influenza vaccination against the spread of the COVID-19 epidemic has been suggested. Methods: We used publicly available data bases to explore the hypothesis as well as the effect of multiple social and environmental factors in the 20 Italian regions. Results: Our results suggest that vaccination against seasonal influenza might beneficially impact on incidence and severity of the novel corona virus epidemic. Population density and vehicular traffic were also moderately associated with cumulative incidence of COVID-19. None of the other variables we considered showed an effect on cumulative incidence, case fatality rate or mortality from COVID-19. Conclusions: Extending influenza vaccination coverage particularly among the elderly, vulnerable individuals with specific chronic medical conditions, health care workers, and workers in other essential services, early in the upcoming 2020 influenza season, might help reduce the health impact of a second epidemic wave of COVID-19.