BA.5の次には、BA.2.75という変異株が控えている？

There's a new COVID-19 Omicron subvariant, so what is BA.2.75 and why are some people calling it 'Centaurus (《天文》ケンタウルス座 / sentɔ́rəs)'?

By Angelica Silva / 2022-07-23 / © 2022 ABC

BA.2.75 has spread rapidly throughout India, Europe and the US.

Since the COVID-19 pandemic first began, many have become desensitised (鈍感にさせる/disénsətàiz) to these next few words:

"There's a new Omicron sub-variant."

BA.2.75 was first detected in India in early May. Since then, it's been found in Europe and the United States.

The chief scientist with the World Health Organization (WHO), Soumya Swaminathan, said BA.2.75 appeared to have mutated in a way that could indicate "major immune escape".

However, Dr Swaminathan says there isn't enough data to know how severe its impact will be.

Here's what we know so far:

What is the BA.2.75 sub-variant?

Adelaide epidemiologist Adrian Esterman says it's "another child of BA.2".

"The fact is, there's no research that shows BA.2.75 is more transmissible or more serious," Professor Esterman said.

In a video posted to the WHO's Twitter account, Dr Swaminathan said BA.2.75 had "not yet officially been named", but that some people were "referring to it as BA.2.75".

"There are still limited sequences available to analyse, but this sub-variant seems to have a few mutations on the receptor binding domain of the spike protein, a key part of the virus that attaches itself to the human receptor," she said.

"We don't know that. So, we will have to wait and see."

Dr Swaminathan said the WHO committee and the Technical Advisory Group on Virus Evolution (TAGVE) are "constantly looking at the data from around the world".

Why are some people calling BA.2.75 'Centaurus'?        Is this official?

Ah, Twitter. Some people have been calling the new variant 'Centaurus', after the Greek father of the mythical Centaurs.

While a catchy name, it's not official. A Twitter user, Xabier Ostale, who is not a virologist, coined the nickname in a tweet.

"If you can do that, you may as well call BA.4 and BA.5 Gemini — the naughty twins."

Should we be worried?

Professor Esterman says that, until more substantive research is done, BA.2.75 remains a variant that is being monitored.

"We simply don't know if it's more transmissible or severe at this stage. If we find that it is, then it will become a variant of concern."

How are the names of sub-variants decided?

Professor Esterman said the original variants of the Sars-CoV-2 virus, which causes COVID-19 infections, were named after the country where they were first discovered.

However, the WHO decided that this wasn't fair on the countries involved.

"Even though it might first be discovered in Brazil, it may have actually started in Colombia," Professor Esterman explained.

"So they decided these names stigmatise the countries too much."

Instead, the WHO began to name variants after letters of the Greek alphabet.

"We had Alpha, Beta, Gamma, Delta and so on," he said.

How did it all start? BA.1, BA.2 and BA.3

Omicron was first identified in late November in South Africa. Since then, it has evolved into a family tree, one that keeps growing.

It started off as three sub-variants, all appearing in late November 2021 in southern Africa: BA.1, BA.2, and BA.3.

Professor Esterman said all three of these were discovered roughly around the same time, in Botswana.

southern Africa (including Botswana) においては、HIV感染者が多く、免疫抑制状態の人々が特に多い。その為、COVIDが一旦感染すると、自己の免疫力で、ウイルスを完全に排除することができず、感染が長期間継続する為、その間に、ウイルスは様々な変異を遂げることになる。

"BA.1 initially took over in Australia and had a massive number of cases. At its peak, we were getting 100,000 cases a day."

Professor Esterman said BA.2 turned out to be more infectious than BA.1, eventually overtaking it.

As for BA.3 — it never really took off.

"Some of the mutations made BA.3 less transmissible. So it pretty much died out," Professor Esterman said.

"What's happened now is that BA.2 has now had children – think of them as grandchildren [of COVID-19]," he said.

Their names? BA.5, BA.4, BA.2.1.2.1 and BA.2.75

When were BA.4 and BA.5 detected?

BA.4 was first detected in January 2022 in South Africa. BA.5 was also detected in South Africa, in February 2022.

"These two are talked about together because they have almost identical mutations," Professor Esterman said.

However, they do differ in some of the mutations on the body of the virus.

"It turns out BA.5 is more infectious than BA.4. [The] majority of the cases in Australia are either of these two."

Risk of long COVID accumulates with reinfection, says Norman Swan.

BA.2.75 Is the Newest Omicron Subvariant—Here's What We Know So Far

Two cases have been identified in the U.S., but it's still too soon to know what kind of impact the subvariant might have here.

By Julia Landwehr / Published on July 14, 2022 / Health

Fact-checked on July 14, 2022, by Marley Hall, a writer and fact checker specializing in medical and health information.

As Omicron subvariants BA.4 and BA.5 become overwhelmingly dominant in the U.S., another new subvariant is also causing concern: BA.2.75.

Dubbed "Centaurus" by a Twitter user, Omicron BA.2.75 was first reported in India, and has now spread to about 10 other countries, the World Health Organization (WHO) said in a Twitter video on July 5.

So far, there have been two recorded cases of the BA.2.75 variant in the U.S., the Centers for Disease Control and Prevention (CDC) confirmed to MedPage Today. The variant has also popped up in the U.K., New Zealand, Australia, and Canada, among others, said Ulrich Elling, a researcher with the Austrian Academy of Sciences, on Twitter on July 3. Elling's Twitter thread showing the variant's steep rise in India turned heads online earlier this month.

The new mutation has been labeled a Variant of Concern Lineage Under Monitoring by the WHO, which means that it's still too early to know whether the BA.2.75 mutation will, like other variants, pose a threat to public health.

Even though it's still early, here's what we know about the BA.2.75 subvariant right now.

How Is BA.2.75 Related to Other Omicron Subvariants?

As its name suggests, BA.2.75 is related to the BA.2 Omicron subvariant, which was the dominant strain in the U.S. from about mid-May to mid-June. If we think of the different subvariants like a family tree, BA.2 is a trunk, and BA.2.75 is a branch off of the trunk, explained Jasmine Plummer, PhD, an assistant professor and associate director of the genomics core at Cedars Sinai Medical Center.

The other branch off of that same trunk is the BA.4 and BA.5 subvariants. The BA.2, BA.2.75, BA.4, and BA.5 are all similar, but have different mutations that still make them unique from one another. These similarities provide a basis for experts to make some kind of predictions about how the BA.2.75 might spread going forward.

The primarily mild symptoms associated with Omicron and its subvariants–cough, fatigue, congestion, and runny nose–mean that the BA.2.75 strain could affect people in a similar way.

"We might have symptoms much, much, much milder, especially for [the] vaccinated, compared to the original or even like Omicron," Plummer told Health. "And so it will present more like a mild version, I think, of past COVID."

BA.2.75 also has mutations on its spike proteins that are similar to the BA.4 and BA.5 subvariants, which Plummer explained could help it evade the immune system more easily. And, she said, BA.2.75 appears to have eight additional mutations that might give it the edge when it comes to replicating and spreading, even as compared to the BA.4 and BA.5 strains.

"Once [BA.2.75] got in, it would be able to replicate faster, which would kind of allow us to get COVID instead of our vaccines kind of being able to fight it off completely," Plummer said.

It's these kinds of mutations and differences in the makeup and behavior of BA.2.75 that could be the cause for most concern, said Bill Morice, MD, PhD, president of Mayo Clinic Laboratories.

"We really got burned with Omicron–which you know, had quite a bit of difference from the Delta strain and really caused a spike," Dr. Morice told Health. "I think when you see a subvariant or variant that has a lot of difference from what's been circulating, then that really raises concern that it will be different enough that it could cause its own kind of unique surge in cases."

The Future of BA.2.75 in the U.S.? Too Early to Call

Despite being able to use other Omicron subvariants as benchmarks, it's important to remember that without significant data about how BA.2.75 works, what we know right now is just a prediction, explains Sumit Chanda, PhD, professor of immunology and microbiology at Scripps Research.

"You have to be careful, because you can't necessarily extrapolate global trends based on a single country," Chanda told Health. "There's no way to know until you do the real world experiment. Even if you do it in animals or so on, it's nearly impossible to model which variants are going to make it and which ones are not."

The other aspect that's important to consider, Chanda added, is that different subvariants compete with each other as they try to spread and avoid the body's immune system. The BA.5 strain is currently doing the best job of that here in the U.S., causing over 65% of all confirmed COVID cases. Only time will tell if BA.2.75 can out compete BA.5 and cause its own wave of new infections, Chanda said.

It seems likely that, because it's related to the BA.4 and BA.5 strains, BA.2.75 will, on some level, be able to evade our immune responses. But it's too early to tell just how protected we might be from previous COVID infections or from vaccines.

"It does look like it might be driving an increase in cases in part of the world that has had a lot of COVID immunity. What it means for us now, we can't know for sure. We're just going to have to watch," Dr. Morice said.

Even though there are a number of unknowns still surrounding BA.2.75, we have tools available to keep us safe, from vaccines to drug treatments like Paxlovid, Chanda said.

"If the preventative measures don't get you there–the boosters, the masking, being a little bit more careful than you usually would–I think there are good fail safes (安全策) here," Chanda said.

Still, the virus is not yet endemic like the flu, even though these new variants seem to be less deadly, Chanda said. We're just not there yet in terms of figuring out how to coexist with COVID.

"Eventually there'll be some sort of predictability in how it [spreads], but right now, it doesn't seem like it's hit that kind of point," Chanda said. "When that's going to be, I have no idea."