Modern DNA sequencing, where available, may permit rapid detection (sometimes known as 'real-time detection') of genetic variants that appear in pathogens during disease outbreaks.[8] Through use of phylogenetic tree visualisation software, records of genome sequences can be clustered into groups of identical genomes all containing the same set of mutations. Each group represents a 'variant', 'clade', or 'lineage', and comparison of the sequences allows the evolutionary path of a virus to be deduced. For SARS-CoV-2, over 330,000 viral genomic sequences have been generated by molecular epidemiology studies across the world (https://en.wikipedia.org/wiki/Variants_of_SARS-CoV-2)

B.1.617.2, the so-called Indian or Delta variant was first discovered in India. Alpha in the UK, Beta in South Africa, Gamma in Brazil.

I know they cried wolf too many times, but that delta variant does seem to be particularly infectious.