From the moment public health officials started to track new variants of coronavirus, it became clear that the same mutations were cropping up time and again and making the virus more troublesome. What are these mutations, what do they do, and what do they mean for the pandemic?
What are mutations?
The genetic code of the coronavirus is held in about 30,000 letters of RNA, a molecule similar to DNA. When the virus infects human cells, the genetic code is copied to make new virus particles. But mistakes happen in the process and these copying errors become mutations in the new virus. Most mutations have little effect, while some will impair the virus and die out. But occasionally a mutation will benefit the virus, for example by making it latch on to human cells more effectively, or evade some of the immune defences the body builds after previous infection or vaccination.
When did coronavirus start to mutate?
The virus has been mutating from the start. On average, a single Sars-CoV-2 virus accumulates two single-letter mutations a month. The influenza virus mutates at about twice this rate. Many of the mutations that happened early on helped the coronavirus adapt to humans. One of the first mutations to go global is known as D614G, or Doug for short. This mutation arose early in the pandemic and by June 2020 it had spread around the world. The D614G mutation stabilises the spike proteins that enable the virus to latch on to human cells and infect them. (Variants without Doug are, naturally, called Douglas).
What other mutations are there?
New mutations emerge all the time, but scientists focus on those that have the potential to make the virus more problematic. One of the most common mutations is N501Y, known as Nelly to geneticists tracking the new variants. This mutation affects the 501st amino acid in the virus, swapping asparagine for another amino acid called tyrosine. This changes the shape of the spike protein in a way that helps the virus bind more tightly to human cells. One likely consequence is that it takes less virus to cause an infection, so the disease spreads more easily.
The mutation appears in at least three variants that are causing concern around the world: the fast-spreading B117 or 501YV1 variant first spotted in Kent; the B1351 or 501YV2 variant first found in South Africa; and the P1 or 501YV3 variant first seen in Brazil.