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. 2022 Mar 11;10(3):426.
doi: 10.3390/vaccines10030426.

Effectiveness of mRNA COVID-19 Vaccination on SARS-CoV-2 Infection and COVID-19 in Sicily over an Eight-Month Period

Emanuele Amodio  1 , Giuseppe Vella  1 , Vincenzo Restivo  1 , Alessandra Casuccio  1 , Francesco Vitale  1 , On Behalf Of The Covid-Surveillance Working Group Of The University Of Palermo  1
Affiliations

Effectiveness of mRNA COVID-19 Vaccination on SARS-CoV-2 Infection and COVID-19 in Sicily over an Eight-Month Period

Emanuele Amodio et al. Vaccines (Basel). .

Abstract

In order to reduce the spread of SARS-CoV-2 infection and the burden of disease, since 27 December 2020, Sicily has introduced a regional COVID-19 vaccination campaign. This study aimed at estimating the effectiveness of mRNA COVID-19 vaccines on SARS-CoV-2 infections and COVID-19. A retrospective cohort study was carried out on 3,966,976 Sicilian adults aged 18 years or more, who were followed-up from 1 January 2021 to 30 September 2021. The risk of SARS-CoV-2 infection, severe COVID-19, and COVID-19 death or intubation during the study period was compared among vaccinated with two mRNA doses and unvaccinated individuals. Cox regression, adjusted for age and sex, and a joint-point analysis on rate trends were performed. 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 4693 (0.12%) severe COVID-19, 277 (0.01%) intubated, and 2649 (0.07%) deaths. After two months from vaccination, adjusted vaccine effectiveness was 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 decreasing effectiveness 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). The study results confirm that mRNA COVID-19 vaccines have high real-world effectiveness, especially in the first months after vaccination. The vaccine effectiveness decreases over time and, even if the decrease is relatively small against severe outcomes, the increasing protection wane suggests the need for booster vaccination campaigns.

Keywords: COVID-19; mRNA vaccines; vaccine effectiveness.

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Conflict of interest statement

E.A., V.R. and F.V. report institutional grants and participation on advisory board from AstraZeneca, MSD and Pfizer Sanofi Pasteur.

Figures

Figure 1
Figure 1
Kaplan–Meier survival analyses on SARS-CoV-2 infection over time in vaccinated and unvaccinated subjects according to the different observation periods ((A): February to September; (B) March to September; (C) April to September; (D) Mayto September; (E) June to September; (F) July to September).
Figure 2
Figure 2
Kaplan–Meier survival analyses on COVID-19 severe cases over time in vaccinated and unvaccinated subjects according to the different observation periods ((A): February to September; (B) March to September; (C) April to September; (D) Mayto September; (E) June to September; (F) July to September).
Figure 3
Figure 3
Kaplan–Meier survival analyses on COVID-19 intubation or death over time in vaccinated and unvaccinated subjects according to the different observation periods ((A): February to September; (B) March to September; (C) April to September; (D) Mayto September; (E) June to September; (F) July to September).
Figure 4
Figure 4
Vaccine effectiveness estimates after adjustment for age and sex according to the different assessed outcomes and follow-up periods. (A) Vaccine effectiveness against SARS-CoV-2 infection; (B) Vaccine effectiveness against severe COVID-19; (C) Effectiveness of vaccines against COVID-19 death or intubation.
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