NEW DELHI (BLOOMBERG) - As India's daily tally of Covid-19 infections surged by a record 200,000-plus cases on two consecutive days, public health experts worry that a new - possibly more virulent - coronavirus variant could be racing through the crowded nation of more than 1.3 billion people.
The new variant, which has a so-called double mutation, is thought to be fuelling India's deadlier new wave of infections that has made it the world's second worst-hit country, surpassing Brazil, and has already begun to overwhelm its hospitals and crematoriums.
The Asian nation has reported more than 14 million Covid cases so far and more than 174,300 fatalities.
"This is a variant of interest we are following," Dr Maria Van Kerkhove, the World Health Organisation's technical lead officer on Covid-19, told reporters on Friday (April 16).
"Having two of these mutations, which have been seen in other variants around the world, are concerning," she said, adding that there was a similarity with mutations that increase transmission as well as reduce neutralisation, possibly stunting the ability of vaccines to curb them.
The new strain underscores the insidious nature of viruses and threatens to thwart containment efforts in India, despite stringent measures such as the world's largest lockdown last year.
An exploding outbreak in India risks undoing a hard-won victory over the pathogen for others too, especially as this strain has now jumped to at least 10 other countries.
Here's what we know so far:
How did the 'double mutation' variant emerge?
The new variant, called B1617, was initially detected in India with two mutations - the E484Q and L452R.
It was first reported late last year by a scientist in India and more details were presented before the WHO on Monday, according to Dr Van Kerkhove.
Viruses mutate all the time, as part of evolutionary biology. Some mutations weaken the virus, while others may make it stronger, enabling it to proliferate faster or cause more infections.
India's health ministry first acknowledged the presence of such a "double mutant" at the end of March, but has downplayed it since.
While it's a variant of interest, it "has not been stamped as a 'variant of concern' so as to say that it is more lethal or more infectious", Dr Aparna Mukherjee, a scientist at the Indian Council of Medical Research, which works under the nation's health ministry, told Bloomberg TV on Friday.
Is it causing the record surge in infections in India?
Genome sequencing indicates that the variant as a possible culprit.
The average prevalence of the variant surged to as high as 52 per cent of samples sequenced in April from almost nothing in January, according to website tracker Outbreak.info, which uses data from global repository Gisaid.
In some districts in Maharashtra state - home to the nation's financial hub Mumbai and epicentre of the current wave that's currently under lockdown-like rules - the prevalence of this variant was more than 60 per cent, according to Dr Anurag Agrawal, director of the state-run Council of Scientific and Industrial Research's genomics institute that's conducting sequencing.
The B1617 was present in samples from about 10 Indian states and while the percentage may vary, it was expected to rise as "it has two critical mutations that make it more likely to transmit and escape prior immunity", Dr Agrawal said.
"We did the maths - we do believe that a lot of the increase in the reproduction number can be explained by these mutations," Dr Nithya Balasubramanian, the head of healthcare research at Bernstein India, told Bloomberg TV this week.
"So, yes, the mutations are a big cause for worry."
After slowly mapping virus genomes in recent months - India did sequencing for less than 1 per cent positive samples as at last month - the country is now scrambling to cover lost ground.
"We are attempting to do at least 5 per cent of whatever samples are there," said ICMR's Dr Mukherjee.
"It looks like that it is spreading faster than pre-existing variants," said Dr Rakesh Mishra, the Hyderabad-based director of the Centre for Cellular and Molecular Biology - another Indian lab doing genome sequencing of Covid samples.
"Sooner or later, it will become prevalent in the whole country, given the way it is spreading."
Has it been found outside India?
This variant has been detected in at least 10 other countries, including the US, the UK, Australia and New Zealand, according to the situation report on outbreak.info.
As at April 16, 408 sequences in the B1617 lineage have been detected, of which 265 were found in India, the report shows.
A surveillance report by the UK government said it has found 77 cases in England and Scotland so far, designating it as a "variant under investigation".
New Zealand has temporarily suspended arrivals of its citizens and residents from India due to the spike in the number returning with Covid-19.
Brazil was also shunned as a Covid-19 superspreader by its neighbours, which were nervous about the virus strain next door.
India's second wave - given its size and rapid pace - will worry other nations that have just about managed their own outbreaks after weeks of economy-devastating lockdowns.
Is it deadlier than other variants out there?
Researchers are still trying to figure that out. The features of the double mutant variant are under investigation, but the L452R mutation is well characterised in US studies, according to Dr Agrawal.
It increases viral transmission by around 20 per cent and reduces antibody efficacy by more than 50 per cent, he said.
Globally, three worrisome variants that have so far emerged in the UK, South Africa and Brazil have caused particular concern.
Studies suggest that they are more contagious, and some evidence points to one of them being more deadly, while another drives re-infections.
The double mutant strain, first found in India, has begun troubling virologists everywhere.
"The B1617 variant has all the hallmarks of a very dangerous virus," Dr William A. Haseltine, a former professor at Harvard Medical School, wrote in Forbes on April 12.
"We must do all that is possible to identify its spread and to contain it."
Do vaccines work against it?
It's hard to know for sure without adequate data and research. India is testing whether the new variants, including the B1617, are capable of "immune escape or not", according to ICMR's Dr Mukherjee.
Immune escape refers to a pathogen's ability to evade human bodies' immunity response.
This means antibodies created after vaccination or prior infection may not protect a person from getting infected.
If the new India variant shows "immune escape" behaviour, this would have deep ramifications for India's vaccination programme, which has picked up after a sluggish start and administered 117 million doses so far.
India has currently authorised three vaccines.
Two of them are already in use, while the third, Russia's Sputnik V, was approved this week. India also fast-tracked approval for foreign vaccines this week.
All of these efforts risk being jeopardised if the shots turn out to be less effective against this double mutation variant.
"It is one of the ones that's on our radar, and in doing so, it means it's on the radar of people around the world," said Dr Van Kerkhove.