© Science Photo Library RFB.1.617.2 has become the newest 'variant of concern' in the coronavirus pandemic - Science Photo Library RF
The new wave of coronavirus in India has hit hard.
Concerns are now mounting over its ramifications for the UK, where cases of the so-called "Indian variant" have more than doubled in a week.
On Friday, Public Health England (PHE) upgraded the variant from "under investigation" to a "variant of concern".
But what does this actually mean? Our Global Health Security team takes a look below.
What is the Indian variant?
There are actually at least three closely related variants coming out of India at the moment, and the decision affects one of them: B.1.617.2. These new variants are being blamed for India's recent catastrophic surge of infections - although there are a number of other factors at play.
What is a 'variant of concern'?
Viruses mutate all the time, and most of these changes have no material effect on the pandemic.
Experts only start investigating if the mutations have "concerning epidemiological, immunological or pathogenic properties", according to PHE.
In plain English, this means asking three questions: does the mutated variant spread more easily? Can it evade previous immunity, either from infection or antibodies? And is it more deadly?
What are the other VoCs?
The answer to at least some of these questions was "yes" for a number of variants that have since caused havoc globally, and which originated in the UK (B.1.1.7), South Africa (B.1.351), and Brazil (P.1).
Why is the Indian variant 'of concern'?
For the Indian variant B.1.617.2., the key concern is transmissibility.
Scientists at PHE believe that it could be at least as contagious as B.1.1.7, which is now dominant in a number of countries, including the UK.
That's what, according to Imperial College immunologist Danny Altmann, makes it a "bona fide variant of concern", or VoC for short.
That's a worry because, as we have seen, more cases means more serious cases - which leads, sadly, to more Covid-19 deaths.
What are the mutations involved, and do they make the virus more deadly?
Like other emerging variants, there is no evidence that the Indian variant is more deadly.
There are other similarities with other VoCs. For example, B.1.617.2 shares a mutation with some other VoCs, called L425R, which may be the reason why it spreads more easily.
Unlike the other variants in the B.1617.2 family, though - which remain "under investigation" rather than "of concern" - it does not have the E484Q mutation. This mutation resembles another known as "Eek", or E484K, which may help the virus evade some types of antibodies.
The presence of these two mutations, among many others, are why the Indian variant family was dubbed a "double mutant" - an essentially meaningless, but headline-grabbing, term.
What about vaccines?
As such, the key question right now is how well jabs will protect against B.1.617.2.
Right now, there isn't much information about this specific variant, scientists say - but recent studies on the other variants, which are similar, hold promising signs.
Prof Altmann, who was involved in one of the studies, said the Indian variant currently looked like "less of a problem" for immune evasion than the Brazilian or South African variants.
And he stressed that the current vaccines continue to provide "good enough" protection against all the existing VoCs.
Vaccine manufacturers are also tweaking vaccines to tackle the variants if needed, and this week the first of these updated jabs, produced by Moderna, successfully neutralised South Africa and Brazilian variants in laboratory trials.
What's the situation in the UK now?
As of Friday 7 May, 520 cases caused by B.1.617.2 have been detected in the UK, mainly in London and the north-west - a significant increase of 318 since the previous data drop.
Clusters have been reported in care homes, though no deaths have been reported, while roughly 10 per cent of cases in London are believed to be caused by B.1.617.2. But this comes from a very low base of infections, and because of data lags, dates from before India became a "red flag" country, stopping international travel, as a PHE epidemiologist Meaghan Kall pointed out on Twitter.
The high proportion of B.1.617.2 detected in the UK could also be as a result of more genomic sequencing - more than half of all positive tests are now sequenced, according to Dr Jeff Barrett, director of the Covid-19 Genomics Initiative at the Wellcome Sanger.
Others are more worried.
Dr Deepti Gurdasani, an epidemiologist at Queen Mary University, said the fast-spreading variant could become dominant in some areas within a fortnight.
"We have seen how quickly a new more transmissible variant can change the shape of the pandemic," she warned on Twitter.
The number of related variants detected is also rising, with 261 cases of B.1.617.1, up by 68, and nine of B.1.617.3.
So what's next?
Designating the Indian variant B.1.617.2 'of concern' in the UK means it triggers surge testing, where teams go door-to-door to try to identify infections to prevent silent spread of the virus by asymptomatic people.
And how concerned should we be?
There are a number of potential scenarios.
The best-case is that infections stay under control thanks to the UK's speedy vaccine roll-out, and the variant has, ultimately, little impact.
But the more worrying scenario is that the new variant takes hold among the communities with low vaccine uptake, where it could cause a major rise in cases and, subsequently, deaths.
For example, while 97 per cent of white over-70 year-olds have had the vaccine, recent figures suggest just 87 per cent of people of South Asian heritage of the same age have done so.
In short, an over-reaction might be better than an under-reaction at this stage.
"We can't afford to be wrong," Professor Ravi Gupta of the University of Cambridge, whose lab is leading research on variants, told The Guardian.
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