The omicron variant of the coronaviruses has been reported in South Africa six weeks after it was first reported.
Does that mean that omicron will not be able to use delta? Will the two strains co-circulate forever?
It looks like omicron's takeover from delta is assured, and that delta is unlikely to reappear in a meaningful way even after omicron has burned through the population. According to an analysis by a biostatistician and biologist at the Fred Hutchinson Cancer Research Center in Seattle, omicron now makes up 99% or more of all coronaviruses infections in many states. Omicron infections began to outnumber delta infections in mid- to late December, according to the genetic sequence collected from COVID-19 patients. The variant is responsible for 80% or more of the cases in states with less omicron.
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Researchers were worried that both omicrons could co-circulate. It was clear that omicron could spread quickly, but it wasn't clear if it was due to an improved ability to spread, or if it was just evading immunity and giving it targets that didn't have it. Omicron does not have immunity. It's two to three times more transmissible than delta, and that's what explains omicron's domination.
"If you put them into direct competition, omicron is going to win, so in the population that is what is going to happen," said Dr. Shiv Pillai, a professor of medicine at Harvard Medical School. "Delta will fade away and omicron will take over, so people will get infections by omicron."
Omicron is less severe than Delta because of a mix of pre-existing immunity in the population and omicron's preference for multiplying in the air passages. If the takeover had continued unimpeded, it could have led to more deaths. An expert told Live Science that the huge wave of omicron infections may provide some protection against future variant and bring us closer to the end of the epidemic. There is a chance of a new variant of the virus with us for the foreseeable future.
There is cross-immunity.
The omicron variant's spike protein has many changes compared to the delta variant. The key to the virus getting into cells is thisProtein, which is also the target of the COVID-19 vaccines.
Even if a person has been exposed to a previous variant of the disease, their immune system will not be able to target the original variant of the disease because they are not well-matched to omicron. There are many different shapes of the same amino acid in the two spikes, according to Pillai. Researchers expect some level of cross-immunity between the two.
A small study from South Africa showed that this cross-re activity is real. The study looked at the immune responses of people who were notvaccinated. Alex Sigal of the Africa Health Research Institute recruited eight unvaccinated and seven vaccine recipients with breakthrough infections. Three of the patients had received two doses of Pfizer's vaccine, three had a single shot of J&J, and one had two shots of J&J.
The researchers took blood from the people four days after they got sick and then again two weeks later. They tested the body's first line of defense: neutralizing antibodies, by exposing coronaviruses in the lab to the blood samples. The antibodies prevent the virus from entering cells.
The blood from two weeks later showed a huge increase in its ability to destroy the omicron in the lab culture. The neutralization of the delta increased as well. Omicron should boost protection against delta.
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This wasn't a surprise, Pillai said. When exposed to the coronaviruses, the immune system will create antibodies that recognize the different parts of the spike. Some of these shapes are the same on both omicron and delta, so some anti-omicron antibodies will fight back against them.
This is the same mechanism as the booster dose of the vaccine. A recent study led by Alejandro Balazs, an immunologist at the Ragon Institute of Massachusetts General Hospital, MIT and Harvard, found that a booster dose of vaccine did not cause neutralization against omicron. The immune system is reintroduced to the original spike protein by a booster. The re-introduction increases the levels of the antibody. Many of the numerous antibodies bind to the same shaped bumps on both omicron and delta. Even if many of the vaccine-generated antibodies aren't shaped for omicron, a high concentration of antibodies against these shapes can still block infections.
When we get boosted, the antibodies to the common bumps protect us.
The dynamics of transmission.
One silver lining of Omicron's dominance is its apparent mildness. Catching omicron is less dangerous than catching delta. The next few weeks will be difficult because the number of omicron breakthrough infections is higher than during the delta wave. The number of patients hospitalized with COVID-19 in the U.S. increased to over 100,000 as of January 6th, beating out the high of 97,811 seen last winter.
The omicron wave will give many people new immunity to the coronaviruses, including cross-reactive immunity that may protect them from the most serious outcomes if another variant does emerge.
The South African study found that people who were previously vaccine-vaccinated had better responses to omicron infections. It is possible that the virus may block the optimal immune response, something vaccination doesn't do. The neutralizing antibodies from vaccination do not last as long.
The data shows that infections can protect you from some infections, but it's not as good when it comes to hospitalization and disease.
A combination of vaccines and omicron could help transition the world from a Pandemic to an endemic state, meaning that most people will have some pre-existing immunity to the coronaviruses and spikes in infections will become less disastrous. People may become vulnerable to serious outcomes as they get further from previous infections or booster shots if immunity fades. It's possible that a more severe immune-evading variant could arise. In the future, Pillai said, Pfizer's Paxlovid, which showed promise in clinical trials, will likely be key for reducing the damage caused by the continued circulation of the disease.
It was originally published on Live Science.
