N440K variant of SARS-CoV-2 has Higher Infectious Fitness

Several variants of SARS-CoV-2 have been emerging across the globe, continuing to threaten the efforts to end COVID-19 pandemic. Recent data indicate the prevalence of variants with N440K Spike substitution in several parts of India, which is under the second wave of the pandemic. Here, we first analyze the prevalence of N440K variants within the sequences submitted from India and identify a rising trend of its spread across various clusters. We then compare the replicative fitness and infectivity of a prototype of this variant with two other previously prevalent strains. The N440K variant produced ten times higher infectious viral titers than a prevalent A2a strain, and over 1000 folds higher titers than a much less prevalent A3i strain prototype in Caco2 cells. Similar results were detected in Calu-3 cells as well, confirming the increased potency of the N440K variant. Interestingly, A3i strain showed the highest viral RNA levels, but the lowest infectious titers in the culture supernatants, indicating the absence of correlation between the RNA content and the infectivity of the sample. N440K mutation has been reported in several viral sequences across India and based on our results, we predict that the higher infectious titers achieved by N440K variant could possibly lead to its higher rate of transmission. Availability of more sequencing data in the immediate future would help understand the potential spread of this variant in more detail.