COVID-19 vaccination effectiveness: one year of observation

Background and Objective: In 2020, Italy was one of the most affected countries in the world, counting over 70.000 deaths for covid-19. The Italian ministry of health led the nationwide vaccination campaign. On 1st september 2021, 72% of the population received at least one dose. We aimed to assess the effectiveness of COVID-19 vaccines regarding infection, admission, days of hospitalization, access to the intensive care unit (icu) and death for one year of observation; to the best of our knowledge, there are no studies with such a long study period. Methods: We conducted an observational retrospective study on all the residents older than 18 of grosseto province (tuscany, Italy) from 1st september 2021 to 31 august 2022. We included who had completed the primary vaccination cycle at the begging of the study and who had never received either one dose by the end of the period. Moreover, all the people who contracted COVID-19 infection before 1 september 2021 were excluded. First, we extracted data regarding vaccine Administrations and reportable COVID-19 tests for all the residents; Then, we linked data of the COVID-19 hospitalizations (the main reason for the admission). We performed logistic and multiple linear regressions adjusting for age, sex, and charlson-comorbity-index with statav17. Results: We observed 213.895 residents and 44.236 COVID-19 cases, and 613 hospitalizations for COVID-19. Considering age, sex and charlson-comorbityindex, the effectiveness of vaccination is high for all the outcomes: admission (adjor 0.22 95%ci 0.19-0.26), uci (adjor 0.49 95%ci 0.26-0.91), death (adjor 0.40 95%ci 0.25-0.65). Moreover, vaccination reduced days of hospitalization (coef. -3.11 95%ci -4.50 to -1.71). However, increasing age, male sex and comorbidities increased the risk of severe outcomes. Conclusion: Our results confirm that vaccination prevents severe disease with hospitalization, admission to uci, and death and it is crucial especially for older male people with comorbidities.