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. 2023 Mar;28(13):2200494.
doi: 10.2807/1560-7917.ES.2023.28.13.2200494.

Risk of SARS-CoV-2 reinfection by vaccination status, predominant variant and time from prior infection: a cohort study, Reggio Emilia province, Italy, February 2020 to February 2022

Massimo Vicentini  1 , Francesco Venturelli  1 , Pamela Mancuso  1 , Eufemia Bisaccia  2 , Alessandro Zerbini  3 , Marco Massari  4 , Andrea Cossarizza  5   6 , Sara De Biasi  6 , Patrizio Pezzotti  7 , Emanuela Bedeschi  2 , Paolo Giorgi Rossi  1 ; Reggio Emilia COVID-19 Working Group  8 ; Members of the Reggio Emilia COVID-19 Working group
Collaborators, Affiliations

Risk of SARS-CoV-2 reinfection by vaccination status, predominant variant and time from prior infection: a cohort study, Reggio Emilia province, Italy, February 2020 to February 2022

Massimo Vicentini et al. Euro Surveill. 2023 Mar.

Abstract

BackgroundUnderstanding the epidemiology of reinfections is crucial for SARS-CoV-2 control over a long period.AimTo evaluate the risk of SARS-CoV-2 reinfection by vaccination status, predominant variant and time after first infection.MethodsWe conducted a cohort study including all residents in the Reggio Emilia province on 31 December 2019, followed up until 28 February 2022 for SARS-CoV-2 first infection and reinfection after 90 days. Cox models were used to compare risk of first infection vs reinfection, adjusting for age, sex, vaccine doses and comorbidities.ResultsThe cohort included 538,516 residents, 121,154 with first SARS-CoV-2 infections and 3,739 reinfections, most in the Omicron BA.1 period. In the pre-Omicron period, three doses of vaccine reduced risk of reinfection by 89% (95% CI: 87-90), prior infection reduced risk by 90% (95% CI: 88-91), while two doses and infection reduced risk by 98% (95% CI: 96-99). In the Omicron BA.1 period, protection estimates were 53% (95% CI: 52-55), 9% (95% CI: 4-14) and 76% (95% CI: 74-77). Before Omicron, protection from reinfection remained above 80% for up to 15 months; with Omicron BA.1, protection decreased from 71% (95% CI: 65-76) at 5 months to 21% (95% CI: 10-30) at 22 months from the first infection. Omicron BA.1 reinfections showed 48% (95% CI: 10-57) lower risk of severe disease than first infections.ConclusionsNatural immunity acquired with previous variants showed low protection against Omicron BA.1. Combined vaccination and natural immunity seems to be more protective against reinfection than either alone. Vaccination of people with prior infection reduced the risk of severe disease.

Keywords: Epidemiology; Immunity; Omicron; Reinfection; Sars-CoV-2.

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Conflict of interest statement

Conflict of interest: None declared.

Figures

Figure 1
Figure 1
Incidence rate of first SARS-CoV-2 infections and reinfections and COVID-19 vaccination coverage in the study population, Reggio Emilia province, Italy, 20 February 2020–28 February 2022 (n = 538,516 individuals)
Figure 2
Figure 2
Risk of SARS-CoV-2 infection by time from the first diagnosis compared with no infection in the pre-Omicron and Omicron BA.1 period, Reggio Emilia province, Italy, 20 February 2020–28 February 2022 (n = 538,516 individuals)
See this image and copyright information in PMC

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