Almost all mutations that do occur are harmless disturbances that do not change the way the virus works – some can damage the virus while a small fraction can make the virus more contagious.
The Delta version has spread around the world, and the next versions are already on the rise. If the goal is to limit infection, then vaccines are the answer. Image credit: Tech2/Abigail Banerjee
increase of coronavirus The variants have highlighted the enormous impact of evolutionary biology on daily life. But how mutation, random chance and natural selection generate diversity is a complex process, and there has been much confusion about how and why new types have emerged.
Until recently, the most famous example of rapid development was black pepper story. In the mid-1800s, factories in Manchester, England began to cover the moth’s habitat with soot, and the moth’s general white coloration made them visible to predators. But some of the moths had mutations that made them darker. Since they were better hidden in their new world, they could avoid predators and breed more than their white counterparts.
we are one evolutionary biologist And a infectious disease epidemiologist at the University of Pittsburgh who work together to track and control the growth of pathogens. For the past year and a half, we have been following closely how coronavirus Has acquired various mutations around the world.
It’s natural to be surprised at being highly effective COVID-19 Vaccines are leading to the emergence of types that evade vaccines – such as the pepper moths that prey on the birds that hunt them. but just under 40 percent of people in the world have received the vaccine – only two percent in low-income countries – and Around one million new infections are occurring every day around the worldThe emergence of new, more infectious forms, such as delta, is being driven by uncontrolled transmission, not vaccines.
How does a virus mutate
For any organism, including viruses, copying its genetic code is the essence of reproduction – but the process is often incomplete. coronavirus They use RNA for their genetic information, and copy RNA DNA is more error-prone than using. Researchers have shown that when coronavirus Repeat, About three percent of new virus copies contain a new, random error., otherwise known as mutation.
each creates an infection millions of viruses within a person’s body, leading to many mutating coronavirus E.s. However, the number of mutated viruses is dwarfed by a much larger number of viruses that are identical to the strain initiating the infection.
Almost all mutations that occur are harmless glitches Those don’t change the way the virus works – and others actually harm the virus. A few small bits of change can make the virus more infectious, but these mutants should be lucky too. To give rise to a new variant, it must successfully pass to a new individual and replicate as many copies.
Transmission is the critical bottleneck
Most viruses in an infected person are genetically identical to the strain from which the infection started. this is very likely that one of these copies – not a rare mutation – gets passed on to someone else. Research has shown that Almost no mutated viruses are transmitted from its original host to another individual.
And even if a new mutant causes infection, the mutant virus usually outnumbers the non-mutant virus in the new host and are not usually transmitted to the next person.
The small odds of a mutant being transmitted is called “population barrierThe fact that it is only a small number of viruses that initiate the next infection is the important, random factor that limits the likelihood that new variants will arise. The birth of every new variant is a chance event in which one Includes copying error and an unlikely transmission event. coronavirus copies in an infected individual, the chances are remote that a fitter mutant is among the few that spread to another individual and become amplified into a new variant.
How do new variants come out?
Unfortunately, the uncontrolled spread of the virus can overcome even the toughest obstacles. While most mutations have no effect on the virus, How contagious some people can be and have grown coronavirus Is. If a rapidly spreading strain is capable of producing a large number of COVID-19 Somewhere, it will begin to compete with less infectious strains and produce a new variant – like the delta variant did.
Many researchers are studying which mutations cause more transmissible variants. coronavirus . It turns out that the variant There is a tendency to have multiple of the same mutation He an increase in the amount of virus an infected person carries. With more than a million new infections occurring every day and billions of people still not vaccinated, there is rarely a supply of susceptible hosts. Therefore, natural selection will favor mutations that can exploit all these illiterate people and create coronavirus more permeable.
Under these circumstances, the best way to inhibit the growth of coronavirus To reduce the number of infections.
Vaccines prevent new forms
The delta version has spread around the world, and The next variants are already on the rise. If the goal is to limit infection, then vaccines are the answer.
Even though vaccinated people can become infected with the delta variant, they experience small, mild infections compared to unrelated individuals. This greatly reduces the chance of any mutated virus – either one that makes the virus more transmissible or one that may allow it to gain previous immunity from vaccines – from jumping from person to person.
After all, when almost everyone has some immunity coronavirus By vaccination, viruses that break this immunity can gain a competitive advantage over other strains. It is theoretically possible that in this situation, natural selection could lead to variants that could infect vaccinated people and cause severe disease. However, these mutants must still survive the population bottleneck.
For now, it is unlikely that vaccine-induced immunity will be the major player in the emergence of the variety because so many new infections are occurring. It is just a numbers game. The slight benefit the virus would have from vaccine theft is Dwarfed by huge opportunities to infect uninfected people.
The world has already seen a connection between the number of infections and the rise of mutants. NS coronavirus It remained essentially unchanged for months until the pandemic spiraled out of control. With relatively few infections, the genetic code had limited opportunities for mutation. But as infection clusters exploded, the virus rolled the dice millions of times and some of the mutations produced fitter mutants.
The best way to prevent new types is to stop their spread, and the answer is vaccination.
von cooper, professor of microbiology and molecular genetics, University of Pittsburgh and Lee HarrisonProfessor of Epidemiology, Medicine and Infectious Diseases and Microbiology, University of Pittsburgh