If researchers predict which coronavirus variant will sweep the world, the Delta variant will not be their first guess.But since its first appearance in India in December 2020, this highly infectious variant has become the main strain of the virus, accounting for more than 90% of new COVID cases in the United States
The emergence of Delta Air Lines has caused many countries to restore travel and mask restrictions that have been relaxed as vaccination rates have risen. Although most of these vaccines seem to be effective against Delta, the large number of cases increases the possibility that it will cause a “breakthrough infection” in the vaccinated population. It is not clear whether it will cause more serious diseases than previously circulating strains.
However, it is clear that Delta has a powerful evolutionary advantage over earlier strains. Vaughan Cooper, an evolutionary biologist at the University of Pittsburgh, said: “Its growth rate is unique in the history of this pandemic.” Now, he and others are trying to figure out why this particular mutation carries a series of different mutations. The variant is so successful.
The rapid spread of the virus may be partly due to the fast replication speed. A recent study found that people infected with Delta have an average of 1,000 times more virus (called viral load) than people infected with the original strain, which allows them to quickly infect more people. The advantage of this variant seems to stem from a combination of mutations in the spike protein: part of the new coronavirus binds to the ACE2 receptor on the cell surface and allows the virus to infect them.
Scientists also want to know whether Delta can escape the human immune system in addition to increased transmission.It lacks a mutation called E484K, which helps many Other variants Partially avoid being neutralized by antibodies. But laboratory studies have shown that the Delta mutation called L452R is even better at performing the same function.
In a recent preprint study that has not yet been published in a journal, the epidemiologist Nathan Grubaugh of the Yale School of Public Health in New Haven, Connecticut, tested 18 different variants The reaction of serum extracted from plasma-plasma is the liquid component of blood-came from 40 fully vaccinated healthcare workers. They found that the participants’ antibodies were able to neutralize Alpha variants well, while Delta was quite good.But they Poor effect For the variants carrying the E484K mutation, such as Beta or Gamma, the variants were first discovered in South Africa and Brazil respectively.
Considering that Delta is much more effective than Beta or Gamma in dissemination, the results of the study are surprising. Although the L452R mutation alone improves immune evasion, the actual Delta virus is actually not that good at it, indicating that the specific combination of mutations on Delta confers unique functions to the virus. “Even if we try to simplify things, it is difficult to figure out which combination will become the next’it’ virus,” Grubaugh said. He said that Delta’s success shows that immune evasion may not give the virus as strong an evolutionary advantage as it is contagious, at least in the unvaccinated population.
But this may not apply to all people. For example, the Gamma variant spread rapidly in Brazil, but rarely spread in other parts of the world. Some researchers suspect that the COVID infection rate in Brazil may be higher than most countries, which means that when Gamma appears, most people have been able to develop a strong immune response. In that population, evading the immune system can help the virus.
Mehul Suthar, a virologist at Emory University in Atlanta, said that the number of mutations that the virus can acquire on the spike protein before it can no longer bind to the ACE2 receptor may be limited. “There is always this tug-of-war between the ability of viruses to spread, spread, and replicate and their ability to evade antibody responses,” he said.
Suthar pointed out that the Kappa variant that appeared in India at about the same time as Delta is the same as most of Delta’s mutations and mutations similar to E484K. But Kappa has not spread around the world, which suggests that these mutations may interact in some way, making the virus unsuitable for evolution. “It was the Delta variant that finally took off, which is a bit surprising,” Suthar said. “This is actually comforting.”
Grubaugh believes that important new spike protein mutations are unlikely. Conversely, the most suitable virus will have a combination of “best” mutations, allowing it to spread widely among most people. But it is difficult to predict what these will be. “I think we have a good grasp of which mutations we should look for, but that doesn’t necessarily mean that if we see these, we know exactly how they behave,” he said.
Cooper agreed. “This combination is logical [of high transmissibility and the ability to evade antibodies] If possible, as long as the number of infections remains high, it will evolve,” he said. The more people who have not been vaccinated, the more likely it is that there will be something worse than Delta.
This potential nightmare virus actually appeared last year: a variant called B.1.620, first appeared in Africa. It carries the E484K mutation, as well as many other spike protein mutations that may increase infectivity. Emma Holdcroft, a genetics researcher at the University of Bern in Switzerland, said: “On this alone, you would say,’Oh my God,'”. But the number of B.1.260 cases quickly dropped. “It’s obviously not as simple as having all these mutations, and you are the worst thing,” Hodcroft said.
Nathaniel Landau, a microbiologist at New York University’s Lange Medical Center, said the good news is that it will be relatively simple to adjust the mRNA vaccines produced by Pfizer and Moderna to make them more effective against this variant. “If there is indeed a variant that can escape better than the current one, then you really need to use booster shots against that variant,” he said.
However, at the same time, the current vaccine is still the best way to prevent the emergence of new variants. “Obviously, with these viruses, it does not mean that if we defeat Delta, we will be able to defeat the pandemic,” Suthar said. “Only the other keeps appearing.” He said that if too few people are vaccinated and the spread of the virus is uncontrolled, “there will be an endless cycle of infection, mutation and transmission.”