RESUMEN
To reconstruct the evolutionary dynamics of the 2019 novel-coronavirus recently causing an outbreak in Wuhan, China, 52 SARS-CoV-2 genomes available on 4 February 2020 at Global Initiative on Sharing All Influenza Data were analyzed. The two models used to estimate the reproduction number (coalescent-based exponential growth and a birth-death skyline method) indicated an estimated mean evolutionary rate of 7.8 × 10-4 subs/site/year (range, 1.1 × 10-4 -15 × 10-4 ) and a mean tMRCA of the tree root of 73 days. The estimated R value was 2.6 (range, 2.1-5.1), and increased from 0.8 to 2.4 in December 2019. The estimated mean doubling time of the epidemic was between 3.6 and 4.1 days. This study proves the usefulness of phylogeny in supporting the surveillance of emerging new infections even as the epidemic is growing.
Asunto(s)
Betacoronavirus/genética , Infecciones por Coronavirus/epidemiología , Infecciones por Coronavirus/transmisión , Genoma Viral , Modelos Estadísticos , Pandemias , Neumonía Viral/epidemiología , Neumonía Viral/transmisión , Secuencia de Bases , Teorema de Bayes , Betacoronavirus/clasificación , Betacoronavirus/aislamiento & purificación , Betacoronavirus/patogenicidad , COVID-19 , Infecciones por Coronavirus/diagnóstico , Infecciones por Coronavirus/virología , Monitoreo Epidemiológico , Evolución Molecular , Humanos , Difusión de la Información , Sistemas de Lectura Abierta , Filogenia , Neumonía Viral/diagnóstico , Neumonía Viral/virología , ARN Viral/genética , SARS-CoV-2 , Alineación de Secuencia , Homología de Secuencia de Ácido NucleicoRESUMEN
SARS-CoV-2 is constantly evolving, leading to new variants. We analysed data from 4400 SARS-CoV-2-positive samples in order to pursue epidemiological variant surveillance and to evaluate their impact on public health in Italy in the period of April-December 2021. The main circulating strain (76.2%) was the Delta variant, followed by the Alpha (13.3%), the Omicron (5.3%), and the Gamma variants (2.9%). The B.1.1 lineages, Eta, Beta, Iota, Mu, and Kappa variants, represented around 1% of cases. There were 48.2% of subjects who had not been vaccinated, and they had a lower median age compared to the vaccinated subjects (47 vs. 61 years). An increasing number of infections in the vaccinated subjects were observed over time, with the highest proportion in November (85.2%). The variants correlated with clinical status; the largest proportion of symptomatic patients (59.6%) was observed with the Delta variant, while subjects harbouring the Gamma variant showed the highest proportion of asymptomatic infection (21.6%), albeit also deaths (5.4%). The Omicron variant was only found in the vaccinated subjects, of which 47% had been hospitalised. The diffusivity and pathogenicity associated with the different SARS-CoV-2 variants are likely to have relevant public health implications, both at the national and international levels. Our study provides data on the rapid changes in the epidemiological landscape of the SARS-CoV-2 variants in Italy.