Co-circulation of SARS-CoV-2 Alpha and Gamma variants in Italy, February and March 2021

BackgroundSeveral SARS-CoV-2 variants of concern (VOC) have emerged through 2020 and 2021. There is need for tools to estimate the relative transmissibility of emerging variants of SARS-CoV-2 with respect to circulating strains.AimWe aimed to assess the prevalence of co-circulating VOC in Italy and...

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Published in:Euro surveillance : bulletin européen sur les maladies transmissibles Vol. 27; no. 5; p. 1
Main Authors: Stefanelli, Paola, Trentini, Filippo, Guzzetta, Giorgio, Marziano, Valentina, Mammone, Alessia, Sane Schepisi, Monica, Poletti, Piero, Molina Grané, Carla, Manica, Mattia, del Manso, Martina, Andrianou, Xanthi, Ajelli, Marco, Rezza, Giovanni, Brusaferro, Silvio, Merler, Stefano
Format: Journal Article
Language:English
Published: Sweden Centre Europeen pour la Surveillance Epidemiologique du SIDA (European Centre for the Epidemiological Monitoring of AIDS) 03.02.2022
European Centre for Disease Prevention and Control (ECDC)
Subjects:
COVID-19
Humans
Italy - epidemiology
Mathematical models
Models, Theoretical
Morbidity
Public health
SARS-CoV-2
Severe acute respiratory syndrome coronavirus 2
Italy
lineage
co-circulation
SARS-CoV-2 variant of concern
transmissibility
ISSN:1560-7917, 1025-496X, 1560-7917
Online Access:Get full text
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Summary:BackgroundSeveral SARS-CoV-2 variants of concern (VOC) have emerged through 2020 and 2021. There is need for tools to estimate the relative transmissibility of emerging variants of SARS-CoV-2 with respect to circulating strains.AimWe aimed to assess the prevalence of co-circulating VOC in Italy and estimate their relative transmissibility.MethodsWe conducted two genomic surveillance surveys on 18 February and 18 March 2021 across the whole Italian territory covering 3,243 clinical samples and developed a mathematical model that describes the dynamics of co-circulating strains.ResultsThe Alpha variant was already dominant on 18 February in a majority of regions/autonomous provinces (national prevalence: 54%) and almost completely replaced historical lineages by 18 March (dominant across Italy, national prevalence: 86%). We found a substantial proportion of the Gamma variant on 18 February, almost exclusively in central Italy (prevalence: 19%), which remained similar on 18 March. Nationally, the mean relative transmissibility of Alpha ranged at 1.55-1.57 times the level of historical lineages (95% CrI: 1.45-1.66). The relative transmissibility of Gamma varied according to the assumed degree of cross-protection from infection with other lineages and ranged from 1.12 (95% CrI: 1.03-1.23) with complete immune evasion to 1.39 (95% CrI: 1.26-1.56) for complete cross-protection.ConclusionWe assessed the relative advantage of competing viral strains, using a mathematical model assuming different degrees of cross-protection. We found substantial co-circulation of Alpha and Gamma in Italy. Gamma was not able to outcompete Alpha, probably because of its lower transmissibility.
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Correspondence: Paola Stefanelli (paola.stefanelli@iss.it)
These authors contributed equally to this article.
These authors contributed equally as senior authors.
ISSN:1560-7917
1025-496X
1560-7917
DOI:10.2807/1560-7917.ES.2022.27.5.2100429