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Early studies suggest omicron is formidable — but not unstoppable

The variant erodes a key line of defense from vaccines, but boosters can help restore protection

A mobile coronavirus vaccine clinic dispenses shots Dec. 7, 2021, in New York. (Andrew Kelly/Reuters)

A sobering portrait of the omicron variant is emerging from the first burst of laboratory studies on the coronavirus’s latest incarnation, showing that the mutated virus can slip past a shield of protection provided by the standard two-shot vaccine regimen.

But the studies, including one released Wednesday by Pfizer and its vaccine partner BioNTech, point to a potential path for slowing omicron’s march: Booster shots could help control the variant by raising virus-fighting antibodies high enough to block the pathogen.

The data is preliminary, and leaves some of the most urgent questions about omicron — including how it will behave in the real world outside of laboratories — unanswered. Collectively, the new research suggests omicron can dodge some of the most important immune defenses triggered by vaccines, but only partially.

As expected, virus-blocking antibodies generated by two shots of the Pfizer-BioNTech vaccine dropped steeply in the face of omicron’s many mutations. But building a higher wall of immune protection appeared to restore protective levels of antibodies. Booster shots are one way to do that. The research also suggests that people who have been infected with the coronavirus and then get the two-shot regimen generate sufficient antibodies to keep omicron at bay.

“With omicron, with these data over the past 24 hours, I’d say it’s unequivocal that boosting for the winter is important,” said Shane Crotty, an immunologist at La Jolla Institute for Immunology who was not involved in the studies released this week. “For the general public, the good news is the boosters are going to work, full stop.”

Anthony S. Fauci, President Biden’s chief medical adviser for the pandemic, said at a Washington Post Live event that “the booster shot could be the answer to the challenge that we’re facing with the omicron.”

“So, if ever there was a clarion call for people who are not vaccinated to get vaccinated, and those who are vaccinated fully to get boosted, the new challenge with the omicron variant clearly is that,” Fauci said.

Scientists warn that the omicron picture is only beginning to come into focus, with a flood of data expected in the next few weeks from inside laboratories and countries where omicron is spreading. Preliminary data suggests it is extremely transmissible, possibly more so even than delta, the variant driving a surge in cases in the United States — and, until omicron came along, the most dangerous variant yet to emerge.

But other questions about this latest coronavirus threat remain unanswered, including whether omicron causes more severe illness than other variants — or even, as some officials including Fauci have suggested, might typically result in a milder case.

Pharmaceutical companies are racing to create and test a revised shot that focuses the immune system’s power on omicron. The companies could ship doses as early as March. But any such move is contingent upon what the science says about omicron and whether government leaders and regulatory agencies signal that a revamped vaccine is necessary.

For now, the laboratory studies outline a potential strategy with existing vaccines: Rely heavily on boosters.

“The message is fairly consistent, because I think the message is that boosters are probably the best thing we can do in the immediate future,” said Benjamin Murrell, a scientist at the Karolinska Institute in Sweden who found a huge variation in how well antibodies from different people blocked omicron.

The need to understand omicron’s true threat is so urgent that data is leapfrogging the usual channels. Papers are being shared even before they are made available on preprint servers, with research findings posted on laboratories’ websites or on Twitter, as Murrell did Tuesday afternoon.

The laboratory experiments offer an early glimpse of how omicron behaves. But such research has limitations. Scientists are exposing the virus, or in some cases a “pseudovirus” that has the superficial features of the virus, to blood samples from people with different levels of vaccination and antibodies. That does not predict, necessarily, how the virus will spread in the general population.

Differences in the experiments and the blood samples being tested mean the public is on the cusp of being deluged with a host of confusing data points.

A South African study of people fully vaccinated with Pfizer-BioNTech shots, for example, showed a fairly consistent 40-fold drop in the ability of antibodies to block omicron. Murrell’s study showed a wide variability, with on average a sevenfold drop in the ability of antibodies to neutralize omicron in samples from 17 blood donors. Pfizer and BioNTech reported a 25-fold drop in their research.

While scientists try to parse the factors that could account for differences, the general takeaway is that antibodies are definitely less adept at blocking omicron than other variants in a laboratory dish.

“There isn’t a perfect correlation between what happens in the lab and what happens in the real world. The real world is a lot more complicated,” said Jacob Lemieux, an infectious-disease doctor at Massachusetts General Hospital and co-lead of a consortium of research institutions studying the coronavirus variants. “How much drop in real-world efficacy are we going to see? No one knows the answer.”

As expected, given the suite of mutations, omicron appears highly — though not completely — able to escape when confronted with antibodies, Lemieux noted. That has implications not only for vaccines, but also for the efficacy of monoclonal antibodies that have been widely used to treat patients ill with covid-19.

Lab experiments that identify declines in antibodies’ ability to block viruses constitute just one piece of the puzzle, and many scientists expect that the other prongs of immunity — including T cells that kill infected cells — will continue to provide a level of protection against severe illness. Many scientists are relieved to see that the virus doesn’t totally escape vaccines’ key line of defense.

“Yes, this is a big drop. What else do you expect? This is a very mutated variant. We cannot expect it does nothing. What was for me the positive message is: I thought it was going to be worse,” said Alex Sigal, a scientist at the Africa Health Research Institute who led the South African study. “The positive message is that existing tools can actually deal with it.”

Özlem Türeci, chief medical officer of BioNTech, said the next steps in controlling the virus would involve expanding use of boosters globally.

“Broad booster campaigns with the current version of our vaccine around the world could help to better protect people and get through the winter season,” Türeci said.

Coronavirus variants like omicron, delta and mu are an expected part of the virus's life cycle, but vaccines can prevent more infectious variants from forming. (Video: John Farrell, Hadley Green/The Washington Post)

One thing is clear: South African scientists’ decision to share their data openly, including the genetic sequence of omicron, helped researchers move at lightning speed in their quest to understand this latest threat.

Typically, scientists seeking to construct pseudoviruses — harmless replicas of the coronavirus — to perform their tests would have to wait for the blueprint of the new spike protein to be synthesized by companies.

But because the South African scientists rapidly shared their data, Swedish public health officials could swiftly identify suspected cases of covid-19 sparked by omicron. That allowed Murrell’s laboratory at the Karolinska Institute to skip some of the laboratory work usually necessary. Instead, after a case was identified, his lab made a clone of the omicron spike from a sample. Results were ready in eight days.

Before Murrell’s lab evaluated results of their experiment Tuesday, Murrell and colleagues expected to see a larger drop in antibodies’ ability to thwart the virus. Instead, they found a wide variation among people and an overall sevenfold drop in protection, which makes omicron worse than delta but not as fearsome as many people expected given the mutations detected on the spike.

While many scientists are encouraged by hints that existing tools could help soften the blow of omicron as it spreads throughout the world, researchers are already looking beyond this variant. Omicron shows that the pandemic has many more chapters to go. Scientists for months had warned about the possible emergence of a variant with mutations that could allow the virus to escape the shields of protection erected by vaccination and earlier exposure.

But many expected to see something similar to delta. Omicron was a whole new beast, surprising even the experts: It had dozens of mutations, not just a handful or two.

“The more depressing part is the virus showing it can have a lot of changes, and so it does look like it’s more flexible than many of us expected,” Crotty said. “This isn’t over with omicron.”

Other coronavirus variants are likely to emerge — and indeed, there are sublineages of omicron with distinct sets of mutations. The virus continues to evolve. Predicting the future of the pandemic is perilous. Scientists don’t know where omicron came from.

One leading theory is that omicron evolved over the course of many months within an immunocompromised patient, someone who could not shake the infection, giving the virus a chance to adapt to therapeutic antibody treatments. Such an accumulation of mutations within a patient has been detected previously but has not been documented as a source of a larger outbreak.

Another possibility is that omicron simply evolved in remote areas that have limited testing and genomic surveillance.

But the most intriguing theory is that it came from an animal, as the result of what is known as reverse zoonosis. In such a scenario, the coronavirus jumps from humans into an animal population, mutates over the course of many months, and then jumps back into humans in a form radically different from any variant previously identified.

It probably won’t be the last time the genetic code of the coronavirus gets a rewrite.

“I think omicron is a wake-up call,” Lemieux said. “If you look at what’s happened over the last two weeks, it looks like, almost out of the blue, a variant emerged that was more transmissible and had the largest drop in neutralizing activity on record. And it has spread in a matter of days throughout the world.”

Frances Stead Sellers contributed to this report.

Coronavirus: What you need to know

Vaccines: The CDC recommends that everyone age 5 and older get an updated covid booster shot designed to target both the original virus and the omicron variant. Here’s some guidance on when you should get the omicron booster and how vaccine efficacy could be affected by your prior infections.

Variants: Instead of a single new Greek letter variant, a group of immune-evading omicron spinoffs are popping up all over the world. Any dominant variant will probably challenge a key line of treatment for people with compromised immune systems — the drugs known as monoclonal antibodies.

Tripledemic: Hospitals are overwhelmed by a combination of respiratory illnesses, staffing shortages and nursing home closures. And experts believe the problem will deteriorate further in coming months. Here’s how to tell the difference between RSV, the flu and covid-19.

Guidance: CDC guidelines have been confusing — if you get covid, here’s how to tell when you’re no longer contagious. We’ve also created a guide to help you decide when to keep wearing face coverings.

Where do things stand? See the latest coronavirus numbers in the U.S. and across the world. In the U.S., pandemic trends have shifted and now White people are more likely to die from covid than Black people.

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