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As of July, 2021, at least four variants of concern are circulating globally in the SARS-CoV-2 pandemic that has resulted in nearly 180 million documented viral infections and almost 4 million COVID-19 deaths worldwide since December, 2019. Variants of concern are lineages that have evolved from the ancestral RNA virus with sufficient mutations to lead to substantial changes in viral characteristics such as increased transmissibility or detrimental change in COVID-19 epidemiology; increased virulence or change in clinical presentation; or decreased effectiveness of public health and social measures, available diagnostics, vaccines, or therapeutics.
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Bekker et al. (2021) studied this question.
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