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JUST one month ago, the world was already struggling to contain the spread of the coronavirus. Now the challenge has become even harder. The emergence of new variants with different properties has changed the rules of engagement.

That the coronavirus should evolve isn’t surprising – this is what viruses do. Scientists have been sequencing the genome of the SARS-CoV-2 virus since it began spreading out of Wuhan in China, recording the mutations that naturally accumulate as more and more people become infected and pass it on.

This virus evolves mercifully slowly. Until recently, the genetic changes we saw were of little…