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Effectiveness of mRNA COVID-19 Vaccination Against SARS-CoV-2 Infection and COVID-19 Disease in Sicily Over an Eight-Month Period
16 Pages Posted: 13 Jan 2022
More...Abstract
Introduction: In order to reduce the spread of SARS-CoV-2 infection and burden of disease, since 27th December 2020 Sicily has introduced a regional Covid-19 vaccination campaign. This study aimed at estimating the effectiveness of mRNA COVID-19 vaccines against SARS-CoV-2 infections and COVID-19 diseases.
Methods: Retrospective cohort study carried out on 3,966,976 adults aged 18 years or more, resident of Sicily and followed-up from 1st January 2021 to 30th September 2021. The risk of SARS-CoV-2 infection, COVID-19 severe disease, and COVID-19 death or intubation during the study period was compared among vaccinated with two mRNA doses and unvaccinated individuals. Cox regression, with adjustment for age and sex, and a joint-point analysis on trends were performed.
Results: Overall, 2,469,320 (62.2%) subjects have been vaccinated and a total of 103,078 (2.6% of the entire population) SARS-CoV-2 positive subjects have been observed including 4,693 (0.12%) severe COVID-19, 277 (0.01%) intubated and 2,649 (0.07%) deaths. After two-month from vaccination, adjusted vaccine effectiveness were 81.3% against SARS-CoV-2 infection, 96.1% against severe COVID-19 and 93.4% against intubation/death. During the eight-month follow-up, statistically significant effectiveness decreasing trends were observed for all the evaluated outcomes (-4.76% per month against SARS-CoV-2 infection; -2.27% per month against severe COVID-19 and -2.26% per month against COVID-19 intubation/death).
Conclusion: Our results confirm that mRNA COVID-19 vaccines have a high real world effectiveness especially in the first months after vaccination. Vaccine effectiveness decreases over time and, although this decrease is relatively less important against severe outcomes, the protection wane seems to support the need for booster vaccination campaigns.
Funding Information: No funds available.
Declaration of Interests: None to declare.
Ethics Approval Statement: The study has been approved by the local A.O.U.P. University Hospital of Palermo, protocol number CEP/2021/08.
Keywords: COVID-19; vaccine effectiveness; mRNA vaccines
Suggested Citation: Suggested Citation