A new Covid-19 mutation has been declared a variant of concern in India after two dozen cases were detected in three states.
The variant, identified locally as 'Delta plus', has showed increased transmissibility.
What do we know about the 'Delta plus' variant and how concerned should we be?
Where has it been discovered?
The variant, identified locally as 'Delta plus', was found in 16 cases in the state of Maharashtra, Indian Federal Health Secretary Rajesh Bhushan told a news conference on Wednesday. The discovery has led to calls to ramp up testing in the affected areas as India struggles to vaccinate its population.
The 'Delta plus' variant, (B.1.617.2) was first was observed on April 5 in India and has been found in several countries. According to Prof Francois Balloux, Professor of Computational Systems Biology and Director, UCL Genetics Institute, UCL, there have been 160 strains of the variant detected worldwide, including in the UK where cases were first discovered in April.
There is no evidence the strain is currently expanding in any country, he said.
How worried should we be?
Prof Balloux, says that at this stage "there is no particular cause for concern".
There are cases in the UK - the first case was observed on April 28, 2021, Prof Balloux says - although they remain at a very low level.
He adds that the 'Delta plus' has remained at extremely low frequency, with the exception of Nepal.
India is on the list of red countries, which means travellers must quarantine in a hotel at a cost of £1,750 for solo travellers.
Restrictions on overseas travel are unlikely to be significantly eased until after all domestic coronavirus restrictions are lifted on July 19.
Is the 'Delta plus' variant more transmissible?
Prof Balloux said that given the tiny number of cases reported, nothing is known about the transmissibility, immune evasion or lethality of the 'Delta plus' variant.
But studies from India have shown the Delta plus variant spreads more easily, binds more easily to lung cells and is potentially resistant to monoclonal antibody therapy, which can help neutralise the virus.
The original Delta variant is around 60% more transmissible than the Alpha variant, and is now the dominant strain in the UK.
The Alpha variant (previously referred to as B.1.17 or the 'Kent variant) was 50% more transmissible than the original strain.
The low frequency of 'Delta plus', Prof Balloux says, suggests it is not more transmissible than Delta.
How is India responding to the latest Covid mutation?
On Monday, India vaccinated a record 8.6 million people as it ramps up its vaccine drive in a bid to outrun the virus.
But, despite the huge numbers jabbed this week, just a tiny fraction (5.5%) of India's 950 million people are vaccinated.
At the current pace, vaccinating the capital New Delhi's population would take a year, experts predict.
India has been administering the AstraZeneca vaccine, made locally by the Serum Institute of India, and homegrown shot Covaxin, made by Bharat Biotech.
Although new infections in India have dropped to their lowest in more than three months, experts say vaccinations should be stepped up because of the transmissibility of new variants.
Over the past 24 hours, India reported 42,640 new infections, the lowest since March 23, and 1,167 deaths.
Infections now stand at 29.98 million, with a death toll of 389,302, health ministry data shows.
Is it normal for viruses to mutate?
Yes. All viruses mutate - some quicker and more efficiently than others.
“SARS-CoV-2, the virus which causes Covid-19 is evolving and mutating all the time, as do all similar viruses," Prof Tom Solomon, the Director of the NIHR Health Protection Research Unit in Emerging and Zoonotic Infections, at the University of Liverpool said.
Many of these mutations will not be significant or causes for concern but some may give the virus an evolutionary advantage which may lead to higher transmission or mean it is more harmful.
Will vaccines work against the 'Delta plus' variant?
It is not yet known. Two doses of vaccines have been shown to be 80%-plus effective against the Delta variant. The more of the population that is vaccinated, the lower levels of transmission are and the fewer opportunities Covid has to mutate.
The longer the vaccination programme lingers, the slower people are to get vaccinated, and so the more opportunities the virus has to find a way around the jab.
Listen to our Covid podcast, Coronavirus: What You Need To Know
Are there other variants?
There have been many genetic variants of Covid-19 identified since the disease was first understood.
For the first 18 months of the outbreak, one dominated, but the virus is under renewed pressure to evolve as so many millions of people have now become infected.