With Covid-19 ravaging the West after first being identified in Wuhan, China back in December, a large effort is being made to trace the current virus back to the original strain and see whether it’s gained any mutations along the way.
In April, a pre-print study found 33 mutations in the SARS-Cov-2 pathogen, suggesting it was mutating quickly. It was believed that the virus could increase its infectivity given the right mutation.
In true 2020 fashion, a preprint published on BioRxiv has now suggested that the strain we’re dealing with currently is not only heavily mutated, but much more infectious.
Mutating to become stronger
Virus mutations, similar to any other organism, happen through random events that can have any number of effects. Most of the time, mutations go unseen or are even bad for the survival of the organism.
A team from the Scripps Research Institute have discovered that mutations in the SARS-Cov-2 strain that is dominant in the West, called G614, has enabled it to multiply more and transmit more efficiently to other hosts. These mutations appear to compensate for a previous weakness that the original strain (D614) had in which the structure on the outside of the virus, called the spike protein, would break off when it attached to human airway cells, stopping it from continuing to be infectious.
The spike protein is involved in attaching the virus cell to the cells of the host, where the virus can go to work on infecting and multiplying before shedding and finding a new host. If the new strain has a mutation that helps it retain the spike protein, it can multiply and infect new hosts at an increased rate. The researchers believe the G614 mutation strain has a more stable spike protein than its D614 counterpart, which may explain why it is so dominant.
As a result, the researchers believe the new strain is around 10 times more infectious than before. Surprisingly though, the increased infectivity doesn't come with an increase in disease severity. Despite an increase of shedding and host-host transmission, patients infected with G614 didn't get more severely affected than those with D614.
The mutations found by the Scripps team correlate with a study released by the University of Sheffield in April, which suggested that mutations were accumulating in the virus through positive selection. In regions with the G614 mutation strain, the researchers noted a "rapid rise in frequency" of the strain and noted it was capable of becoming the dominant strain in just weeks.
Don’t panic though – these studies are preprints and as yet haven’t gone through the rigorous peer-review phase to confirm their results. Scientists have also predicted this would happen, and the team at Sheffield was quick to quell any fear caused by their findings.
“Coronaviruses generate mutations as part of their normal replication. That some of these would have an effect on virus properties is not surprising,” Prof. Ian Jones, professor of Virology at the University of Reading, who was not involved in the study, explained.
Some believe coronavirus mutations might add a few challenges to creating a vaccine, as mutations may change how effectively our immune cells can recognize infection. This is the problem with seasonal influenza (flu) vaccines, as hypermutation of the virus' surface proteins allow it to evade vaccine antibodies. However, scientists don't believe this to be the case with coronavirus, and with positive results coming from early-stage trials of the Pfizer vaccine and others, it looks like they are right.