Genomic Analysis of Early SARS-CoV-2 Variants Introduced in Mexico.

Taboada, Blanca; Vazquez-Perez, Joel Armando; Muñoz Medina, José Esteban; Ramos Cervantes, Pilar; Escalera-Zamudio, Marina; Boukadida, Celia; Sanchez-Flores, Alejandro; Isa, Pavel; Mendieta Condado, Edgar; Martínez-Orozco, José A; Becerril-Vargas, Eduardo; Salas-Hernández, Jorge; Grande, Ricardo; González-Torres, Carolina; Gaytán-Cervantes, Francisco Javier; Vazquez, Gloria; Pulido, Francisco; Araiza Rodríguez, Adnan; Garcés Ayala, Fabiola; González Bonilla, Cesar Raúl; Grajales Muñiz, Concepción; Borja Aburto, Víctor Hugo; Barrera Badillo, Gisela; López, Susana; Hernández Rivas, Lucía; Perez-Padilla, Rogelio; López Martínez, Irma; Ávila-Ríos, Santiago; Ruiz-Palacios, Guillermo; Ramírez-González, José Ernesto; Arias, Carlos F

The COVID-19 pandemic has affected most countries in the world. Studying the evolution and transmission patterns in different countries is crucial to implement effective strategies for disease control and prevention. In this work, we present the full genome sequence for 17 SARS-CoV-2 isolates corresponding to the earliest sampled cases in Mexico. Global and local phylogenomics, coupled with mutational analysis, consistently revealed that these viral sequences are distributed within 2 known lineages, the SARS-CoV-2 lineage A/G, containing mostly sequences from North America, and the lineage B/S containing mainly sequences from Europe. Based on the exposure history of the cases and on the phylogenomic analysis, we characterized fourteen independent introduction events. Additionally, three cases with no travel history were identified. We found evidence that two of these cases represent local transmission cases occurring in Mexico during mid-March 2020, denoting the earliest events described for the country. Within this local transmission cluster, we also identified the H49Y amino acid change in the Spike protein. This mutation is a homoplasy occurring independently through time and space, and may function as a molecular marker to follow on any further spread of these viral variants throughout the country. Our results depict the general picture of the SARS-CoV-2 variants introduced at the beginning of the outbreak in Mexico, setting the foundation for future surveillance efforts.IMPORTANCE Understanding the introduction, spread and establishment of SARS-CoV-2 within distinct human populations is crucial to implement effective control strategies as well as the evolution of the pandemics. In this work, we describe that the initial virus strains introduced in Mexico came from Europe and the United States and the virus was circulating locally in the country as early as mid-March. We also found evidence for early local transmission of strains having the mutation H49Y in the Spike protein, that could be further used as a molecular marker to follow viral spread within the country and the region.