CO-CIRCULATION OF SARS-COV-2 ALPHA AND GAMMA VARIANTS IN ITALY, FEBRUARY AND MARCH 2021

Authors   Stefanelli P, Trentini F, Guzzetta G, …, Severini S, …, COVID-19 National Microbiology Surveillance Study Group

Abstract     Background: Several 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. Aim: We aimed to assess the prevalence of co-circulating VOC in Italy and estimate their relative transmissibility. Methods: We 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. Results: The 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. Conclusion: We 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.

Publish Date  2022

Volume   27 (5)

ISSN    1560-7917

DOI   doi.org/10.2807/1560-7917.ES.2022.27.5.2100429

URL   https://www.eurosurveillance.org/content/10.2807/1560-7917.ES.2022.27.5.2100429

Journal   Eurosurveillance

Pages   Article no. 2100429

PMID   35115077