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An elderly woman receives a coronavirus vaccine in Pittari, Italy

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THE vaccine strategy most nations are following – of vaccinating the most vulnerable first rather than those who are likeliest to spread the coronavirus – may be the best way to save lives in the short term. But it is also the strategy with the greatest risk of driving the evolution of variants that can escape vaccine protection, according to a model developed by Julia Gog at the University of Cambridge.

“What is the absolutely worst strategy? You vaccinate all of the vulnerable and none of the ‘mixers’,” Gog said in an …