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OOne of the main reasons the Delta variant has triggered new outbreaks of Covid-19 infections across the United States is its remarkable ability to copy itself.
This skill has helped make Delta much more transmissible than any other iteration of the coronavirus seen so far. But its replication prowess could also be at the heart of other twists Delta has thrown into the pandemic, including increased breakthrough infections with the variant and why it potentially causes severe Covid-19 more often.
Delta’s dizzying overgrowth isn’t her only tip linked to the increase in infections – and symptomatic infections – in those vaccinated. With the mutations that the variant picked up as it evolves, it can partially mask itself from the antibodies of the immune system. This gives the variant a better chance of sneaking past that first line of defense to trigger infection compared to earlier forms of the virus. (However, the vaccines haven’t lost any important steps in protecting against the severe consequences of the coronavirus. They also still fully prevent many infections.)
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But experts say a crucial factor in the spread of Delta, even among people who have been vaccinated, is that people infected with the variant appear to “shed” relatively massive amounts of the virus, exposing others to much higher levels. a often cited statistic is that, with Delta, people have 1,000 times more virus in their upper respiratory tract at the onset of their infections compared to the strain that emerged in China in 2019. Some experts quibble with this exact estimate, but the fact remains that people who contract Delta have many more viruses in their nose and throat and in turn emit many more viruses. This influx of viruses into the airways of others appears to be able to overwhelm the antibodies that aim to protect cells from infection.
Jeremy Kamil, a virologist at Louisiana State University Health Shreveport, offered an analogy. “It’s like trying to light a wet pile of hay on fire,” he explained. The body’s immune system keeps the tinder moist, but if you throw more and more sparks on that wet hay, “one of them ends up catching.”
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Delta also appears to be particularly susceptible to cracking cells to trigger infection. Once it has gained a foothold it begins to produce copies of itself, like the viral version of the brooms in “The Sorcerer’s Apprentice,” which can then infect neighboring cells, rapidly increasing the viral load beyond that. of what other variations can do and beyond the body’s initial response.
“It only takes entering a few cells to trigger a cascade of infection events,” Kamil said.
As the virus enters more cells it can cause symptoms, which is why you’ve probably heard friends or family say how sick they felt for a few days after having contracted a breakthrough infection. But soon after the onset of infection, the immune system – driven by the vaccine (or a previous infection) to recognize and fight the coronavirus – engages the big guns, with an attack of additional antibodies and immune cells. that can eliminate the virus before it leads to more serious consequences. Therefore, even though Delta causes infections in some vaccinated people, in almost all cases it only causes moderate illness – the purpose for which the injections were designed.
There are other factors besides Delta’s traits that are likely contributing to the increase in breakthrough infections, experts warn. On the one hand, mitigation efforts have largely expired and people have resumed their social lives, leaving us more likely to come into contact with the virus.
Beyond that, it was always going to be difficult to completely remove a pathogen that first infects the upper respiratory tract. The strong immune response generated by vaccines that so powerfully protects people against severe Covid-19 is much more difficult to generate and maintain in the nose and throat.
“It’s a tall order to ask for an injection in your arm to protect the cells in your nose or mouth,” said immunologist Michal Tal, affiliated with Stanford and MIT.
In addition, the antibodies generated by vaccines, which are the body’s first line fighters in trying to block infections, pass months before they are immunized. This is what happens with antibodies in general, and does not mean that person are more sensitive to contract a serious illness. But it does mean that people could be more vulnerable to infection months after their last dose.
“The combination of less antibody and the virus that gets into cells so quickly,” helps explain the increase in breakthrough infections, said Stanley Perlman, longtime coronavirus researcher at the University of Iowa.
It’s a different story for people who aren’t vaccinated and don’t have immune protection. And some research has indicated that, among these people, Delta is more likely to cause illness severe enough to send them to hospital than earlier forms of the virus – although the evidence is mixed.
A to study from the UK, for example, found that people infected with Delta were twice as likely to be hospitalized as those infected with the Alpha variant, which was echoed by research outside Denmark. A to study outside of Norway, however, found no such difference, and a report of the Centers for Disease Control and Prevention noted last week that “it is not clear whether the Delta variant causes more severe disease in adult or pediatric populations.”
The researchers note that it is difficult to compare the severity of the disease across the pandemic and from one variant to another, given all the variables involved: the demographics of those infected, the burden on the health system, improving care over time, and more. And many experts argue that the cases overwhelming hospitals in some states are just a reflection of the virus’ uncontrolled spread, nothing in particular about this version.
Corn if Delta causes serious illness more frequently than other forms of the virus, one possible explanation is how quickly its levels are skyrocketing, experts said. If there are such high levels of the virus in the nose and throat, it is believed, then it is more likely that the virus could enter the lungs, which is the time when more serious consequences. can occur.
“If you have a lot more virus in your nose, why don’t you also have a lot more virus in your lungs?” Said Perlman.
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