Pirola variant: Early lab tests suggest new Covid-19 variant BA.2.86 may be less contagious and less immune-evasive than feared

CNN
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Scientists around the world are fast-tracking lab experiments to try to understand the highly mutated BA.2.86 variant of the virus that causes Covid-19. Results just beginning to emerge are offering some reassurance, experts say.

Two groups — one in China and one in Sweden — have publicly reported results, and more are expected as early as Monday from the United States. So far, early results paint BA.2.86 as more of a paper tiger rather than the looming beast it first appeared to be, although that impression could change as more results come in.

BA.2.86, also known by the nickname Pirola, captured the world’s attention because it looks radically different than any other variants of the coronavirus that we’ve seen so far.

This new lineage has more than 30 changes to its spike protein compared with both its next closest ancestor, BA.2, and compared with the recently circulating XBB.1.5 lineage. It was an evolutionary leap on par with the one the original Omicron variant, BA.1, made when it first appeared almost two years ago — and everyone remembers how that went down.

During the Omicron wave, infections and hospitalizations hit their highest points of the pandemic in the United States. Weekly deaths reached their second-highest peak, a lesson in how even a tamer version of the virus can be a serious threat if it causes a tidal wave of infection across the population. The vaccines had to be updated.

Omicron quickly overtook other Covid-19 variants and began creating its own offshoots — viruses that we’re still dealing with. It became a lesson in how agile the virus can be and how fragile our defenses are in the face of such large shifts.

The White House was worried enough about another Omicron-level event that it quietly polled about a dozen experts earlier this year about the chances the world would see one within the next two years. Most experts pegged the possibility between 10 and 20%.

So when BA.2.86 appeared on the scene in late July with eerie echoes of Omicron, variant hunters were spooked, and researchers leapt into action to learn more about the new lineage. It has spread to at least 11 countries so far, including the United States.

The country reporting the most sequences so far is Denmark, and experts say they are closely watching the situation there for clues to its growth.

But so far only about three dozen sequences, from as many infected patients, have shown up in a global repository over the last month.  Even with a lot less genetic surveillance than we once had, experts think if BA.2.86 were coming on strong, it would be apparent.

“My friends, this is not the second coming of Omicron. If it were, it is safe to say we would know by now,” Dr. Bill Hanage, an epidemiologist who is co-director of Harvard University’s Center for Communicable Disease Dynamics, said in a social media post.

Now, scientists are in the midst of lab experiments — either using copies of the actual virus isolated from patients, or with models of its spike proteins grafted onto the body of a different virus — that are meant to help us better understand how well our immune systems and vaccines will recognize and defend against viruses in the BA.2.86 family.

In the first series of experiments, using the blood of vaccinated mice and from vaccinated and recently infected people, researchers in China determined that BA.2.86 does look really different to our immune systems compared with previous versions of the virus that causes Covid-19, and it is able to escape some of our immunity.

Researcher Yunlong Cao from the Biomedical Innovation Center at Peking University said he saw a twofold drop in the ability of our immunity from vaccination and recent infection to neutralize the BA.2.86 virus compared with viruses from the XBB.1.5 family.

A twofold drop isn’t wonderful, but it’s also not huge. By comparison, an eightfold drop in the ability of vaccine-created immunity to neutralize a new influenza virus is the benchmark scientists use to update the flu shot.

At the same time, the BA.2.86 virus was about 60% less infectious than XBB.1.5 viruses, something that experts think could explain why it has been found in so many different countries, but only at low levels.

“I would say it will slowly circulate in the population. It will not be able to compete with other fast prevailing variants,” Cao noted in an email to CNN, referring to variants like EG.5 and FL.1.5.1, which are the variants that are currently dominating transmission in the United States.

In a second set of experiments, researchers at the Karolinska Institute in Sweden pitted BA.2.86 against antibodies in the blood of human donors that were collected at two different points in time, from late 2022, before the XBB variant emerged, and from late August.

The antibodies in the older samples couldn’t effectively shut down BA.2.86, but the blood samples taken from donors just a week ago did a better job.

“Overall, it doesn’t appear to be nearly as extreme a situation as the original emergence of Omicron,” wrote principal researcher Benjamin Murrell in a post on social media.

“It isn’t yet clear whether BA.2.86 (or its offspring) will outcompete the currently-circulating variants, and I don’t think there is yet any data about its severity, but our antibodies do not appear to be completely powerless against it,” he wrote.

Both of these studies have limitations. Researchers were testing pseudoviruses, which are essentially models of what the BA.2.86 virus looks like, and not the virus itself. The study from Sweden used only a small number of samples from blood donors. And because these studies used blood donors in China and Sweden, they may not reflect the immunity of people in the U.S., who may have been infected with a different mix of variants and immunized with different vaccines.

Still, experts said they were encouraged by these early results and eager to see more in the coming days.

“The news is better than I was expecting,” said Dr. Ashish Jha, former White House Covid-19 response coordinator in part in a post on social media. “And makes me more encouraged that the new upcoming vaccine will have a real benefit against current dominant variant (EG.5) as well as BA.2.86.”

The Variant Technical Group at the UK’s Health Security Agency met last week to consider whether BA.2.86 should be reclassified from a “variant under monitoring” in that country to a “variant of concern.”

In an update posted Friday, the group concluded BA.2.86 doesn’t meet their definition of a variant of concern since they don’t have any evidence that its profile represents a harmful change to its biological properties or a growth rate suggesting it would move at least as fast or faster than currently circulating variants.

The group said two samples of the virus are being cultured in the UK and that data from those lab experiments are likely to be at least 1-2 weeks away.  Meanwhile, they said they are watching for results from international partners.

They, like the rest of the world, are waiting for BA.2.86 to show its hand.