Specific features of the infection caused by SARS-CoV-2 variants in Vero cell culture.

Variants of SARS-CoV-2 differ in pathogenicity. Vero E6 cells are used to isolate, propagate, and study many viruses, including SARS-CoV-2. The aim of this work is to evaluate morphological differences during infection, and their relationships with the dynamics of viral titer. The cytopathic effect of the SARS-CoV-2 Wuhan-like variant was found to mainly follow an apoptotic pattern in 83 ± 6.1% of the cells. Infection resulted in near complete destruction of the cell monolayer. The maximum titer of the Wuhan variant reached 6.2 ± 0.2 log10 TCID50/ml on 4 d.p.i. At an inoculation dose of 3.5 log10 TCID50/ml. During infection with the delta variant (infection dose 4 = log10 TCID50/ml), up to 30% of cells remained alive, and cell death was accompanied by the formation of necrotic foci involving 41 ± 7.8% cells, and apoptosis of 30 ± 9.4% cells, with maximum titer reaching 5 ± 0.3 log10 TCID50/ml on day 5. In case of Omicron infection (infection dose = 3 log10 TCID50/ml), 90% cells survived, and for the rest 10% of cells the infection followed the classical pattern of apoptosis. At 5 d.p.i., the monolayer remained well preserved, but the morphology of all cells was changed suggested a wide infection of Vero cell culture with the Omicron variant. The maximum titer was 4.2 ± 0.3 log10 TCID50 on day 5. The higher doses were preferable for virus replication with Wuhan-like and Omicron viruses infection. For delta variant lower dose showed more effectivity as necrotic pattern of cell death was observed.