Christina Animashaun/Vox

 A slightly more transmissible variation of Covid-19 can be much more dangerous.

A more contagious SARS-CoV-2 virus is a deadlier one. Not because it gets any individual sicker but because it reaches more people. More illness means more cases: more mild cases, more severe cases, more long-term complications, more hospitalizations, and more deaths.

There’s no one perfect estimate for how much more contagious the SARS-CoV-2 variant called B.1.1.7, which was first discovered in the UK, might be. There needs to be more careful lab work done in animals to nail it down, which could take a few more weeks. But preliminary estimates find it to be between 30 percent and 70 percent more contagious. This variant is now popping up all over the world: in the US, throughout Europe, in Asia, and elsewhere. It’s especially concerning, considering that, in the