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Will Omicron erase delta forever?

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Six weeks after being first reported in South Africa on November 24, the omicron variant of the coronavirus is sweeping the previous delta variant.

Does this mean that omicron will erase the delta for good? Or will the two strains co-circulate forever?

Increasingly, it looks like omicron’s takeover of delta is secure – and delta is unlikely to resurface in any meaningful way, even after omicron burns the population down. In many states, omicron now accounts for 99% or more of all coronavirus infections, according to an analysis by Trevor Bedford, a biostatistician and biologist at the Fred Hutchinson Cancer Research Center in Seattle. Bedford and his colleagues were tracking genetic sequences collected from COVID-19 patients and found that omicron infections started to outnumber delta infections from mid-December to the end of December. Even in states with relatively less omicron, the variant is responsible for 80% or more of cases, Bedford wrote on Twitter Jan.5.

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When the omicron first appeared, researchers feared the two variants could co-circulate. It was clear that omicron could spread like wildfire, but it was not clear if this was due to a better intrinsic spreading capacity, or if omicron was simply escaping immunity in people who had been vaccinated and previously infected. , giving him targets that Delta didn’t have. It turns out, however, that omicron escapes immunity. But it is also inherently two to three times more transmissible than delta, which explains the global dominance of omicron.

“If you put them in direct competition, omicron is going to win, so that’s what’s going to happen in the population,” said Dr. Shiv Pillai, professor of medicine at Harvard Medical School who studies the immune system. “People will be more likely to be infected with omicron than with delta, so delta will slowly go away and omicron will take over.”

Omicron is generally less severe than delta, thanks to a mixture of pre-existing immunity in the population and the preference of omicron to multiply in the bronchi, or respiratory tract, rather than in the lungs. This means that its takeover could ultimately result in fewer deaths than if Delta had continued its unhindered assault. And the huge wave of omicron infections could ultimately provide some protection against future variants and bring us closer to the end of the pandemic, an expert told Live Science. Still, the possibility of new variants exists and some form of virus will be with us for the foreseeable future.

Cross immunity

The omicron variant spike protein exhibits dozens of changes in its proteins compared to the delta spike protein. This protein is the key that the virus uses to get into cells; it is also the target of antibody generated by the Vaccines against covid-19.

This means that even if a person has been infected with a previous variant or has been vaccinated, their immune system will not produce well-suited antibodies to omicron; their antibodies are instead primed to target the spike protein of the original variant of SARS-CoV-2 (which is more similar to delta than to omicron). However, there are still many forms of amino acids in common between the two tips, Pillai told Live Science. So, researchers expect some level of cross-immunity between the two.

A small study from South Africa, which has not yet been peer reviewed, has shown that this cross-reactivity does exist. The study looked at immune responses in vaccinated and unvaccinated people infected with omicron. The researchers, led by Alex Sigal of the Africa Health Research Institute in Durban, recruited eight unvaccinated and seven vaccinated participants with breakthrough infections. Three of the vaccinated patients had received two doses of Pfizer vaccine, three had received a single injection of J&J and one had two injections of J&J.

The researchers drew blood from the infected people about four days after the onset of their illness, and then again two weeks later. They then exposed the coronavirus in the lab to blood samples, testing the body’s first line of defense: neutralizing antibodies. These antibodies bind to the virus, preventing it from entering cells.

Unsurprisingly, compared to blood drawn initially, blood two weeks later showed a 14.4-fold increase in its ability to neutralize omicron in a laboratory culture of the virus. But delta neutralization also increased, increasing 4.4 times. This means that an omicron infection should also strengthen the protection against delta.

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It wasn’t surprising, Pillai said. When exposed to the coronavirus, the immune system creates antibodies that recognize the shape of different parts of the spike protein. Some of these forms are the same on omicron and delta, so some anti-omicron antibodies will fight against delta as well.

This is the same mechanism by which a booster dose of the vaccine works, Pillai added. A recent study led by Alejandro Balazs, an immunologist at the Ragon Institute of Massachusetts General Hospital, MIT and Harvard, and published on the Preprint Database MedRxiv found that while two doses of the vaccine elicited no neutralizing ability against omicron, a booster dose combated the variant, and with a response only four to six times weaker than against the original coronavirus strain. This is remarkable, given that a boost again introduces the immune system to the original spike protein. But this reintroduction increases very high antibody levels, Pillai said. A fraction of these many antibodies are cross-reactive – they bind to similarly shaped bumps on omicron and delta. A high enough concentration of antibodies to these shared forms can still block infection, even though many antibodies generated by the vaccine are not designed for omicron.

“It’s the antibodies against these common bumps that protect us when we’re being boosted,” Pillai said.

Transmission dynamics

Omicron’s apparent softness over Delta is a silver lining of its dominance. In a given person, catching omicron is probably less dangerous than catching delta (especially for the vaccinated). However, the absolute number of breakthrough infections of omicron is higher than during the delta wave, which means that the next few weeks will be difficult: the general crushing of those infected at the same time still weighs on health resources at the same time. delta wave level or worse. . According to Our world in data, there were 119,661 hospital patients with COVID-19 in the United States as of January 6, beating the peak of the delta wave of 97,811 and approaching last winter’s peak of 133,268.

But in the coming months, the omicron wave will also give many people new immunity to the coronavirus, including cross-reactive immunity that could protect them from the most serious consequences if another variant emerges.

However, the South African study also highlights why the so-called “natural immunity” of omicron alone is not enough to protect people from reinfection or new variants. The study found stronger antibody responses to omicron infection in previously vaccinated people and more variable responses in unvaccinated people – in some cases the infection induced strong antibody responses and in others, fairly weak responses. (This may be because the virus can activate proteins that turn off or block the optimal immune response – which vaccination does not.) Neutralizing antibodies to infection also decrease over time, as do neutralizing antibodies. vaccination.

“The hard data will tell you that infection can protect you against infection to some extent, but when it comes to hospitalization and illness, it’s not as effective,” Pillai said.

Ultimately, Pillai said, a combination of vaccines and omicron could help turn the world from a pandemic to an endemic state, which means most people will have pre-existing immunity to the coronavirus and as the peaks of infection will become less disastrous in terms of hospitalization, serious illness and death. Nonetheless, the drop in immunity likely means that a certain version of the coronavirus persists and people can become vulnerable to serious consequences as they move away from a previous infection or booster vaccines. It is also possible that a more severe immune evasion variant may appear. In the future, Pillai said, antiviral drugs such as Pfizer’s Paxlovid, which has shown promise in clinical trials, will likely be the key to reducing damage from the continued circulation of SARS-CoV-2.

Originally posted on Live Science