What makes the Omicron variant spread so easily?

The Omicron variant arrived in the United States just around Thanksgiving. Less than a month later, it’s the country’s dominant strain of coronavirus, accounting for 73% of new infections over the past week, according to the Centers for Disease Control and Prevention.

How did this happen? Infectious disease experts say there are two key factors that determine how quickly a virus spreads: how easily it’s transmitted and how well it evades the body’s defenses.

Early research suggests that Omicron has advantages in both areas. However, the data also suggest that the variant’s higher transmission rate has not resulted in more hospitalizations or deaths.

Preliminary results from a Dec. 14 study led by Alejandro B. Balazs of the Ragon Institute in Cambridge, Massachusetts, found that Omicron was twice as contagious as the Delta variant and four times more contagious than the original virus. This study, which has yet to be peer-reviewed, was based on a relatively small sample of 239 patients in and around Boston, so the results may not be representative of Omicron’s behavior in general.

Nonetheless, said Dr. David Pride, an infectious disease specialist at UC San Diego, “you just look at it [the current situation] epidemiologically we know that something is different this time.”

With so many unvaccinated people out there, he added, “it was only a matter of time before we would see a mutated version of the virus that was just better at infecting vaccinated people.”

It’s practically an evolutionary imperative, said Jasmine Plummer, a researcher at Cedars-Sinai Medical Center in Los Angeles who was part of the team that discovered the epsilon variant of the virus last winter.

“Variants arise because viruses try to survive,” Plummer said. “All viruses evolve to avoid their host. So we knew an Omicron was coming.”

And here we are.

Fast replication

One secret of Omicron’s success appears to be its ability to replicate rapidly. Researchers at the University of Hong Kong reported that Omicron “infects and multiplies 70 times faster” in the bronchus, the main airways to the lungs, compared to Delta. Its advantage over the original virus is even greater, they added. The difference was evident only 24 hours after infection.

If this is indeed the case, it means that people infected with the Omicron variant will have many more viruses lodged in their throats, waiting to be expelled into the air when they exhale – and especially when they cough or sneeze. It also suggests that they may be contagious sooner, which would also speed up the spread of the disease.

A potentially helpful sign from the Hong Kong research: Omicron moved more slowly from the throat to the lungs. In their experiments, the scientists found that the new strain replicated in the lungs at less than a tenth the rate of the original virus. This “may indicate a lower severity of the disease,” according to the university.

Pride said Omicron spreads more easily in homes, suggesting the virus is more easily spewed into the air. Another possibility is that a smaller amount of Omicron is required to trigger an infection, he said.

We still don’t know much about how the Omicron variant is transmitted, but the CDC expects that “anyone with Omicron infection can transmit the virus to others, even if they are vaccinated or have no symptoms.”

As Pride put it differently, “We know this disease spreads through humans, so the only way to be reasonably sure you won’t get it is to stay away from humans.”

The spike protein

The coronavirus that causes COVID-19 uses a spike-shaped protein on its surface to enter healthy cells and use them to make copies of itself. Vaccines available in the United States stimulate the production of antibodies that recognize this spike protein and target it for destruction by the body’s immune system.

Omicron has an unprecedented number of spike-affecting mutations. About three dozen were counted by Balazs and his team, and their position suggests they make it harder for antibodies to recognize an Omicron virus particle. That’s true whether the antibodies were generated by a vaccine or a previous infection, they wrote.

Researchers from the University of British Columbia in Canada studied the omicron proteins affected by these mutations at the molecular level. They found that the changes overall allowed the spike protein to bind to human cells more tightly than the original coronavirus could. They published their findings on BioRXiv, a website where scientists gather feedback on preliminary work.

Sriram Subramaniam, the study’s senior author, said in an interview with the university that even small changes in the spike protein “have potentially large implications for how the virus is transmitted, how our bodies fight it off, and the effectiveness of treatments.” ”

He added, “Our experiments confirm what we’re seeing in the real world — that the omicron spike protein is much better than other variants at … evading the immunity generated by both vaccines and natural infections.” ”

Subramaniam said it is noteworthy that vaccine-induced immunity to Omicron is more effective than immunity from a previous infection in unvaccinated patients. This is another sign “that vaccination remains our best defense against the Omicron variant,” he said.

But this defense may not be very effective without a booster.

Balazs’ study found that the protection afforded by vaccination or a previous coronavirus infection was “dramatically reduced” against Omicron. The only exception was people who had recently received a booster dose of the vaccine; According to the study, “They exhibited strong neutralization of omicron.”

This may help explain why “breakthrough” cases and reinfections appear to be increasing rapidly. A South African research team on December 2 reported more than 35,000 COVID-19 reinfections among the 2.8 million people who had tested positive in the past three months.

https://www.latimes.com/science/story/2021-12-23/what-is-it-about-the-omicron-variant-that-makes-it-spread-so-easily What makes the Omicron variant spread so easily?

Russell Falcon

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