- Coronavirus pandemic
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We're back in familiar territory – growing concern about a new variant of coronavirus.
The latest form is the most heavily mutated version discovered so far – and it has such a long list of mutations that it was described by one scientist as "horrific".
The confirmed cases are mostly concentrated in one province in South Africa, but there are hints it may have spread further.
Immediately there are questions around how quickly the new variant spreads, its ability to bypass some of the protection given by vaccines and what should be done about it.
There is a lot of speculation, but very few clear answers.
So, what do we know?
The variant is called B.1.1.529 and is likely to be given a Greek code-name (like the Alpha and Delta variants) by the World Health Organization on Friday.
It is also incredibly heavily mutated. Prof Tulio de Oliveira, the director of the Centre for Epidemic Response and Innovation in South Africa, said there was an "unusual constellation of mutations" and that it was "very different" to other variants that have circulated.
"This variant did surprise us, it has a big jump on evolution [and] many more mutations that we expected," he said.
In a media briefing Prof de Oliveira said there were 50 mutations overall and more than 30 on the spike protein, which is the target of most vaccines and the key the virus uses to unlock the doorway into our body's cells.
Zooming in even further to the receptor binding domain (that's the part of the virus that makes first contact with our body's cells), it has 10 mutations compared to just two for the Delta variant that swept the world.
But a lot of mutation doesn't automatically mean: bad.
A mutation is the virus trying out something new that may or may not help it. You have to look at what those mutations actually do.
Some of these have been seen before in other variants, which allows you to take a punt at their likely role in this variant.
For example N501Y seem to make it easier for a coronavirus to spread. There are others in there that make it harder for antibodies to recognise the virus and might make vaccines less effective, but there are others that are completely new.
Prof Richard Lessells, from the University of KwaZulu-Natal in South Africa, said: "They give us concern this virus might have enhanced transmissibility, enhanced ability to spread from person to person, but might also be able to get around parts of the immune system."
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However, it is the whole package – the sum of every mutation – that matters.
There have been many examples of variants that have seemed scary on paper, but came to nothing.
"The full significance is still uncertain," said Prof de Oliveira.
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Scientific studies in the laboratory will yield give a clearer picture, but answers will come more quickly from monitoring the virus in the real world.
It is still early to draw clear conclusions, but there are already signs that are causing worry.
There have been 77 fully confirmed cases in Gauteng province in South Africa, four cases in Botswana and one in Hong Kong (which is directly linked to travel from South Africa).
However, there are clues the variant has spread more widely.
This variant seems to give quirky results (known as an S-gene dropout) in the standard tests and that can be used to track the variant without doing a full genetic analysis.
That suggests 90% of cases in Gauteng may already be this variant and it "may already be present in most provinces".
But it tells us nothing about whether it spreads faster than Delta, is any more severe or can evade the immune protection that comes from vaccination.
It also does not tell us how well the variant will spread in countries with much higher vaccination rates than the 24% of South Africa that is fully vaccinated.
So for now we are left with a variant that raises concerns and clearly needs to be watched closely, but critical questions remain impossible to answer for now.
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