Mutations, immunity and vaccines

Less than two years ago, the world was happily floating along, dangerously ignorant of the existence of a coronavirus that would soon turn life on earth upside down.

Since the SARS-CoV-2 virus blew up into the global consciousness, a lot has been learned about this new very aggressive menace. But many key questions, like why humans respond so differently to this virus, continue to torment scientists.

Some people who contract SARS-2 never know they are infected, others have flu-like symptoms, some recover completely, others go on to suffer from the condition known as “long Covid” and some … die.

The question is, what predisposes different individuals to those various outcomes?

Angela Rasmussen, a virologist, wrote: “To me, the data (and all the virus research) suggests the host response is a major determinant, if not THE major determinant, of disease severity.” She questions why some immune systems are able to easily handle the virus whilst others submerge.

How much immunity is enough immunity and how long will it last?
Scientists are trying to establish how much immunity is enough to determine who is protected and who needs to have their immunity boosted.

It is considered that beyond specific antibody levels, physiological factors that vary from individual to individual are relevant and this is one of the factors that helps to explain why there is so much variability in people’s susceptibility to the virus and the severity of disease they experience.

Knowing how long immunity lasts, after infection and after vaccination, would allow for better use of vaccines and tell us how achievable herd immunity is, and if and when vaccine booster shots will be needed.

It could be that protection against infection is comparatively short-lived, but protection against severe disease is longer lasting and it could be that vaccine-induced protection has a different durability than infection-induced protection.

Up to now, the vast majority of people who contracted Covid have not caught it again. Reinfections will occur as this coronavirus is like the other four human coronaviruses that cause colds, but no one knows how often it will happen or if it will be milder. The question is if we are heading for a situation like what occurs with the seasonal coronaviruses, necessitating constantly updated vaccines to keep viral prevalence and disease low.

Viral variants and the battle against Covid-19
The variants are the major worry for experts as these have changed the virus in disadvantageous ways. Some made it more transmissible, others appear to, at least partially, evade the immune protections generated by previous infection or immunisation.

We question what impact these variants will have on vaccine-related protection, effective treatment and what impact this virus will have on our world in years to come.

As increasing numbers of people have some protection, either from previous infection or vaccination, the virus will have to evolve to continue to be able to infect people. Knowing more about this will help with decisions on when and how to update vaccines.

Why and how new variants emerge
The huge number of active coronavirus infections offers plenty of opportunity for mutations to occur and new variants to arise.

There has been a lot of confusion about why and how new variants emerge.

It is natural to wonder if highly-effective COVID-19 vaccines are leading to the emergence of variants that evade the vaccine. But with just under 40% of people in the world having received a dose of a vaccine (only 2% in low-income countries) and nearly a million new infections occurring globally every day, uncontrolled transmission with massive numbers of new COVID–19 infections are the main drive for the emergence of new, more contagious variants, like Delta, not vaccines.

Coronaviruses use RNA to store information, and small changes in that genetic code can lead to new strains of the virus. For any organism, copying its genetic code is the essence of reproduction although this process is often imperfect. Researchers have shown that when the coronavirus replicates, around 3% of new virus copies have a new, random error, known as a mutation.

Each infection produces millions of viruses within a person’s body, leading to many mutated coronaviruses.

Nearly all of the mutations that occur are harmless but, even if a small fraction of changes may make the virus more infectious, these mutants must be lucky as, to give rise to a new variant, it must successfully jump to a new person and replicate many copies.

Most viruses in an infected person are genetically identical to the strain that started the infection. It is much more likely that one of these copies, not a rare mutation, gets passed on to someone else.

The birth of every new variant is a chance event involving a copying error and an unlikely transmission event. Out of the millions of coronavirus copies in an infected person, the odds are remote that a fitter mutant is among the few that spread to another person and become amplified into a new variant.

Although most mutations have no effect on the virus, some can and have increased how contagious the coronavirus is and by out-competing less contagious strains will generate a new variant, just like the Delta variant did.

With more than a million new infections occurring every day and billions of people still unvaccinated, susceptible hosts are rarely in short supply. So, natural selection will favour mutations that can use the unvaccinated people to make the coronavirus more transmissible.

Stoping new variants
The Delta variant has spread around the globe, and the next variants are already on the rise. Even though vaccinated people can still get infected with the Delta variant, they tend to experience shorter, milder infections than unvaccinated individuals. This greatly reduces the chances of any mutated virus from jumping from one person to another.

The world has already witnessed the relationship between the number of infections and the rise of mutants. The coronavirus remained essentially unchanged for months until the pandemic got out of control. With relatively few infections, the genetic code had limited opportunities to mutate. But as infection clusters exploded, fitter mutants were produced.

The best way to stop new variants is to stop their spread.

The answer to that is vaccination … for everyone!

Best health wishes,
Maria Alice