As SARS-CoV-2, the virus that is causing the COVID-19 pandemic, continues to propagate through the world, it also accumulates mutations. Mutations play an extremely important role in the progression of a disease and its severity, and a regular monitoring of the mutations may go a long way in mitigating a pandemic.
Recently, one such mutation analysis of the novel coronavirus has been done in Houston that comprises over 5,000 COVID-19 patients. The study, published in the peer reviewed journal mBIO, reported that a mutation in the spike protein of the virus has become dominant. The mutation, D614G, was found in the largest study of SARS-CoV-2 virus in a city.
According to the paper, the mutation is an outcome of a neutral drift and the response our immune system generates against the virus. The neutral drift refers to the random genetic changes occurring in the virus which don’t account for any special benefit to the virus, neither do they harm it. During the initial wave of the pandemic this particular mutation accounted for almost 71% of the novel coronaviruses that were identified in the patients of Houston. But, during the second wave virus, this particular mutation rose upto a staggering 99%. This is significant as it shows that the D614G mutation outnumbers the other viral strains.
This finding is also a reflection of another important study done in July. In a study published in Cell, the analysis of some 28,000 viral genome sequences from across the world was conducted and it was found that the D614G mutation was dominating at a global scale. During the initial time, in February and March, the D614G strain was not the dominating strain, but slowly it picked up and began to dominate all other strains.
Now, the question that appears is why the strain with the said mutation others and how. One idea is that the particular mutation renders the virus more infectious. One UK study that analysed 25,000 genome sequences of the novel coronavirus reported to have found that the virus with the mutation tends to transmit a bit faster in comparison to those without the mutation. This way the mutated virus could cause larger clusters of infections. The logic behind this, apparently, is that natural selection will favour the virus strains that have more infectious capability.
But, not all scientists accept this hypothesis. Some of them have even proposed other explanation, namely the founder’s effect. According to it, the D614G mutation was more common in strains that reached Europe and North America early during the pandemic. This provided them an edge on outcompeting other strains.
The D614G mutation has been found to have occurred in the spike protein, the protein that helps the virus to bind to the ACE2 receptor present in our cells.
Nevertheless, the D614G is not the only mutation that the virus is accumulating. The spike protein is also gathering mutations with unknown significance. A team at the Houston Methodist hospital and University of Texas, Austin that also contributed to the mBIO paper said that one such mutations at the spike protein allowed it to evade neutralising antibodies that are produced by our immune system. This might offer the virus an edge of evading our immune surveillance, but it is not sure whether this mutation allows a rapid transmission among individuals. However, this mutation is rare and surely this is good news.
“The virus continues to mutate as it rips through the world. Real-time surveillance efforts like our study will ensure that global vaccines and therapeutics are always one step ahead,” said Finkelstein, one of the authors of the mBIO paper.
Other mutations were found to be of not much significance, as the scientists found and it could be thought that these are just random changes on part of the viral genome.