Rapid Global Spread of the SARS-CoV-2 Delta (B.1.617.2) Variant: Spatiotemporal Variation and Public Health Impact

Abstract

The COVID-19 pandemic has already affected human society for more than 1.5 years. As of August 8, 2021, this pandemic had caused more than 203 million infected and 4.3 million deaths worldwide. As an RNA virus, SARS-CoV-2 is prone to genetic evolution, thus resulting in development of mutations over time. Numerous variants of SARS-CoV-2 have been described globally, four of which are considered variants of concern (VOCs) by the WHO: Alpha (B.1.1.7), Beta (B.1.351), Gamma (P1) and Delta (B.1.617.2). The Delta VOC was first reported in India in December of 2020 and has since affected approximately 130 different countries and regions. Herein, the spatiotemporal spread of the Delta VOC during April to July 2021 in 20 selected countries with available data were analyzed. The prevalence of the Delta VOC sequences was maintained at low levels in the beginning of April, increased rapidly in the following 3 months and is now becoming the predominant viral strain in most regions of the world. We also discuss the effects of the Delta VOC on transmissibility, clinical severity and vaccine effectiveness according to the latest data. The Delta VOC has greater transmissibility and risk of hospitalization than the ancestral SARS-CoV-2 strains and the other three VOCs. The Delta VOC places partially or unvaccinated sub-populations at high risk. Currently authorized vaccines, regardless of vaccine type, still have reliable effectiveness against symptomatic infections and hospitalizations due to the Delta VOC.