COVID-19
Mutations and variants of SARS-2.
- Does the SARS-2 virus mutate rapidly?
- Do all mutants produce the same amount of virus?
- Could mutants escape the antigen-specific immune response?
Does the SARS-2 virus mutate rapidly?
No, coronaviruses mutate less than other RNA viruses but with the current world-wide incidence still many mutants will occur.
- In general RNA viruses mutate rapidly but coronaviruses are an exception to the rule since they have a proof-reading RNA-dependent RNA polymerase.
- It might be contra intuitive that a virus should limits is evolvability by proof reading against mutations. I suspect it might be attributable to its crucial ability to limit innate immune responses in all mutants in an individual.
- Nevertheless, the world has adapted a deviant anti-epidemic strategy that allows the SARS-2 virus to cause over 200 million cases in humans and thus to evolve many mutants. And in many regions of the world this spreads on.
Do all mutants produce the same amount of virus?
No, the recent virus variants have higher virus concentration and are more infectious.
- The Alpha-variant (B.1.1.7 or British variant) has 10-fold higher virus titers. The Delta variant (B.1.617.2 or Indian variant) has 1000-fold higher virus titers. Higher virus loads allow the virus to spread easier. Mutants can yield higher virus concentration because of:
- stronger binding the receptor,
- use of an alternative receptor (not observed yet), and
- by decreasing the innate immune response.
- At the onset of symptoms, virus titers rapidly decline but disease might still occur.
Could mutants escape the antigen-specific immune response?
No, the recent virus variants have higher virus concentration and are more infectious.
Yes, mutants might specifically escape T-cell or antibody responses.
- Evolutionary pressure would allow escape mutants to reinfect people without sterilizing immunity.
- In the first few months after infection, there would be selective pressure for mutants that would escape antibody responses to allow them to infect other people.
- Considering its epidemiological mechanisms, this would mainly occur in populations with very high virus circulation.
