All viruses mutate over time, it is a common occurrence in nature. This is no different for SARS-CoV-2, the virus that causes COVID-19. SARS-CoV-2 has had thousands of mutations since the original virus sequence was first identified a year ago. Most of the time, these mutations do not change the behavior of the virus and are considered “temporary” mutations that the virus carries with it as it continues to spread.
However, from time to time, some of the mutations turn out to be beneficial for the virus. Depending on where they occur, it can help the virus become more infectious and spread more quickly, or it can help the virus better escape from the immune system, making it less detectable. Several new variants of SARS-CoV-2 have recently been described, and many alarms have been raised due to the fact that the virus started to behave differently from the original variants, apparently becoming more transmissible and / or less detectable.
Now, new research from the University of Pittsburgh School of Medicine has shown that SARS-CoV-2 may be selectively excluding fragments of the genetic sequence that encodes an important part of the virus, the spike protein on its surface. The spike protein is used by the virus to attach itself to cells and infect them, and this is also the part of the virus that is targeted by antibodies, allowing the immune system to detect the virus and remove it.
“You can’t fix what’s not there,” said senior study author Paul Duprex, PhD, director of the University of Pittsburgh’s Vaccine Research Center in a statement. “Once it disappears, it disappears and, if it disappears in an important part of the virus that the antibody ‘sees’, it disappears forever.”
The study, published in the journal Science, shows how small deletions of fragments in the genetic code responsible for the structure of the spike protein are causing it to become more resistant to neutralizing antibodies. This results in a form of adaptive evolution, as the virus review mechanism that should normally detect these errors during replication and correct them is not capturing fragment deletions, which results in a permanent change in the SARS-CoV- 2, and this is changing the evolution and behavior of the virus.
Several antibodies (green and red) bind to the SARS-CoV-2 spike protein inside cells (blue) when there are no deletions (LEFT). The deletions of the peak protein prevent the neutralizing antibody from binding (absence of green), but other antibodies (red) still attach very well (RIGHT). Recurrent exclusion generates variants that escape neutralization. Image credit: Kevin McCarthy and Paul Duprex