What makes the Delta covid-19 variant more infectious?
Covid cases are on the rise in England, and a fast-spreading variant may be to blame. B.1.617.2, which now goes by the name Delta, first emerged in India, but has since spread to 62 countries, according to the World Health Organization. Delta is still rare in the US. At a press conference on Tuesday, the White Houses chief medical advisor, Anthony Fauci, said that it accounts for just 6% of cases. But in the UK it has quickly overtaken B.1.1.7also known as Alphato become the dominant strain, which could derail the countrys plans to ease restrictions on June 21. The total number of cases is still small, but public health officials are watching the variant closely. On Monday, UK Secretary of State for Health and Social Care Matt Hancock reported that Delta appears to be about 40% more transmissible than Alpha, but scientists are still trying to pin down the exact numberestimates range from 30% to 100%. They are also working to understand what makes it more infectious. They dont yet have many answers, but they do have hypotheses. All viruses acquire mutations in their genetic code as they replicate, and SARS-CoV-2 is no exception. Many of these mutations have no impact at all. But some change the viruss structure or function. Identifying changes in the genetic sequence of a virus is simple. Figuring out how those changes impact the way a virus spreads is trickier. The spike protein, which helps the virus gain entry to cells, is a good place to start. How Delta enters cells  To infect cells, SARS-CoV-2 must enter the body and bind to receptors on the surface of cells. The virus is studded with mushroom-shaped spike proteins that latch onto a receptor called ACE2 on human cells. This receptor is found on many cell types, including those that line the lungs. Think of it like a key fitting into a lock. Mutations that help the virus bind more tightly can make transmission from one person to another easier. Imagine you breathe in a droplet that contains SARS-CoV-2. If that droplet contains viruses with better binding capabilities, they will be more efficient at finding and infecting one of your cells, says Nathaniel Landau, a microbiologist at NYU Grossman School of Medicine. Scientists dont yet know how many particles of SARS-CoV-2 you have to inhale to become infected, but the threshold would likely be lower for a virus that is better at grabbing onto ACE2.