COVID-19 Vaccination Effectiveness in the General Population of an Italian Province: Two Years of Follow-Up

Abstract

We carried out a cohort study on the overall population of the province of Pescara, Italy, to assess the real-world effectiveness of SARS-CoV-2 vaccination against infection, severe, or lethal COVID-19, two years after the start of the vaccination campaign. We included all the resident or domiciled subjects, and extracted the official demographic, vaccination, COVID-19, hospital and co-pay exemption datasets from January 1, 2021, up to February 15, 2023. Cox proportional hazards analyses were adjusted for gender, age, diabetes, hypertension, COPD, major cardio- and cerebrovascular events, cancer, and kidney diseases. Throughout the follow-up (466 days on average), 186,676 subjects received greater than or equal to three vaccine doses (of ChAdOx1 nCoV-19, BNT162b2, mRNA-1273, NVX-CoV2373, or JNJ-78436735), 47,610 two doses, 11,452 one dose, and 44,989 none. Overall, 40.4% of subjects were infected with SARS-CoV-2. Of them, 2.74% had severe or lethal (1.30%) COVID-19. As compared to the unvaccinated, the individuals who received greater than or equal to one booster dose showed a ≥85% lower risk of severe or lethal COVID-19. A massive impact of vaccination was found among the elderly: 22.0% of the unvaccinated, infected individuals died, as opposed to less than 3% of those who received greater than or equal to three vaccine doses. No protection against infection was observed, although this finding was certainly influenced by the Italian restriction policies to control the pandemic. Importantly, during the Omicron predominance period, only the group who received at least a booster dose showed a reduced risk of COVID-19-related death.

Predictors of SARS-CoV-2 Infection and Severe and Lethal COVID-19 after Three Years of Follow-Up: A Population-Wide Study

“…In partial agreement with preliminary findings from the same cohort [25], we also observed a positive association between vaccination with two doses and SARS-CoV-2 infection, while a single dose, as well as one or more booster doses, were associated with a reduced risk. This counterintuitive finding, however, needs to be interpreted with caution.…”

“…Third, as compared to unvaccinated individuals, adjusting for age, gender and for all the recorded comorbidities, those who received any dose of the SARS-CoV-2 vaccine showed a substantially lower risk of both severe and lethal COVID-19, with a clear dose-response trend for both outcomes. Finally, the individuals who received one or more booster doses showed an approximate 50% reduction in the risk of SARS-CoV-2 infection, but a higher rate of infections was observed among the subjects who received only two vaccine doses, in line with previous findings on the same population [25]. Notably, however, when the analyses were restricted to the Omicron predominance period, only the subjects who received two or more vaccine doses showed a significantly lower risk of severe or lethal COVID-19, and vaccination did not protect from infection.…”

“…Age was also independently, inversely associated with the risk of infection: higher rates were observed among younger or adult individuals (<60 years), and the association remained stable after disentangling the role of the other predictors. Different behaviors across age-classes are consistently identified as the possible underlying explanation of the phenomenon [13,30], and prior evidence from the same cohort showed a decreasing trend of infections with increasing age, irrespective of vaccination status and number of vaccine doses [13,25]. However, some studies from both European and non-European countries suggested that the risk of SARS-CoV-2 infection is around 30% lower among adolescents (10-20 years) as compared to older ages [30,31].…”

All-Cause Mortality According to COVID-19 Vaccination Status: an analysis of the UK Office for National Statistics Public Data

“…The results found for the RRs of the first and second doses are confirmed in other studies, e.g. in two studies carried out in an Italian province [11,12]. Both studies show a significantly higher risk of 10 death from all causes for those vaccinated with one and two doses compared to the unvaccinated.…”

Risk of SARS-CoV-2 Reinfection 3 Years after the Start of the Pandemic: A Population-Level Observational Study

“…For all reinfections, we also calculated the proportions of severe and lethal COVID-19. The main analyses were also repeated twice, separately considering the pre-Omicron predominance period (approximately from the start of the follow-up to 31 December 2021) and the Omicron predominance period (approximately from 1 January 2022 to the end of follow-up) [20]. The analyses referring to the pre-Omicron period were restricted to the subjects who had a positive swab before 17 November 2021 (to account for a minimum of 45 days between the first and second infection), and the subjects who had a second positive swab after 31 December 2021 were reassigned to the group without a reinfection.…”