When the coronavirus pandemic was in its infancy, one of the common silver linings scientists mentioned was the virus’s slow rate of mutation. It raised the hope that the virus lacked the agility to rapidly evolve around human immunity – whether from previous infection or vaccine. The virus is certainly slow to mutate by some standards. Sars-CoV-2 typically acquires two single letter changes in its genetic code a month, about half the rate seen in influenza.
So why are so many new variants emerging? At the heart of the problem is the fact the global pandemic is raging. Every new case is a chance for mutations to arise, spread and build up. In the simple arithmetic of evolution, when a virus mutates and gains an advantage it can rise above the others.
Scientist calls for curbs on UK arrivals to halt South African Covid variant
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A particular feature of the Kent variant, named B117, is that rather than emerging gradually, mutation by mutation, it appeared out of the blue with 17 mutations. One theory is that it arose in a single patient who, perhaps because of an impaired immune system, harboured the infection for months – long enough for the more transmissible variant to evolve inside them. Other variants spotted first in South Africa and Brazil may have similar histories, but patchy genomic surveillance makes their origins hard to confirm.
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