VIRUSES EVOLVE through natural selection. Whenever they replicate, changes can creep into their genetic material. If advantageous, these will cause variants sporting them to prosper. One consequence is that such variants spread rapidly. Predictably, then, new variants of SARS-COV-2, the virus that causes covid-19, have started to appear around the world. Four are particularly worrying. One, detected first in Britain, in September, is believed to be 30-50% more transmissible than the original wild-type virus. A second, identified in South Africa a month later, has been linked to higher viral loads in throat and nasal swabs. That makes it easier for it to spread. Two others emerged in America (July) and Brazil (December). And this week a variant of the British variant has also been detected, now sporting a mutation also found in the South African variant. There is no strong evidence to suggest that any of these new variants is more deadly than the wild type, but researchers are worried about the risk of one or more of them evading existing vaccines.
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