What allows the variants of SARS-CoV-2 detected in the UK, South Africa, and Brazil to spread so quickly? How can current COVID-19 vaccines better protect against them? A new study led by researchers at Harvard Medical School and Boston Children’s Hospital helps answer these urgent questions. The researchers focused on a genetic change shared by all three variants called the D614G mutation. It’s known to alter the genetic code of the SARS-CoV-2 spike protein by changing a single amino acid “letter.”