A genomic analysis of more than 45,000 complete SARS-CoV-2 genome sequences was published in this week's Communications Biology, revealing the existence of multiple substrains of the virus in the US, some of which have the potential to become more infectious. In the study, researchers from Michigan State University use SNP calling and other techniques to analyze the SARS-CoV-2 genomes and uncover evidence of four substrains and 11 prevalent missense mutations in the US.