Indian officials say they're closely monitoring "Delta Plus," a version of the Delta coronavirus variant with an extra mutation.
Dr Anurag Agarwal, director at one of India's sequencing labs, said it wasn't "worrisome yet."
"Delta Plus," also called AY.1, accounts for just 0.00002% of all Delta variants sequenced.
Indian health officials have ramped up coronavirus testing and public health measures in three states, following concerns about a new strain of the virus they call "Delta Plus" - but experts worldwide say they're not concerned.
The Indian government said Wednesday that it was closely monitoring "Delta Plus," also known as AY.1, which is the Delta variant of the coronavirus, but with an extra mutation. The original Delta variant is about 60% more infectious than the Alpha variant - the most common version of the virus in the US - and has now spread to at least 75 countries.
"All Delta sub lineages are treated as a variant of concern, although properties of AY.1 are still being investigated," the Indian government said. A "variant of concern" is a virus with mutations that make it more dangerous.
Dr. Anthony Fauci, President Joe Biden's chief medical advisor, said Wednesday that Delta now accounts for at least 20% of infections in the US, and was the "greatest threat" to the nation's efforts to eradicate the disease.
According to the Indian government, AY.1 was first discovered in India on April 5. There have been 40 confirmed cases of the new variant in more than 45,000 sequenced tests in three Indian states - Maharashtra, Kerala and Madhya Pradesh. The officials advised that these states ramp up testing and strengthen "appropriate public measures."
As of June 16, there were 161 confirmed AY.1 infections reported across at least 10 countries, including Canada, India, Japan, Nepal, Poland, Portugal, Russia, Switzerland, Turkey, and the US, according to Public Health England (PHE).
Experts aren't convinced that AY.1, with its extra mutation, is any worse than the original Delta variant.
Professor Francois Balloux, director at the Genetics Institute at University College London, told Insider that the virus was constantly changing, even within a variant.
"Each lineage, of which Delta is an example, is getting about two mutations each month, so it's difficult to predict which mutations will become a concern," he said. Balloux said that AY.1 represents 0.00002% of all Delta variants sequenced to date, and that there was no evidence that the strain was expanding in any country.
The World Health Organization (WHO) told Insider that it was tracking AY.1 as part of the Delta variant, as it does for other variants of concern with additional mutations. "For the moment, this [AY.1] variant does not seem to be common," it said.
PHE, the public health body in the UK, where Delta now accounts for more than 90% of new infections, told Insider that it was investigating the significance of the extra mutation. But there was no evidence that the mutation made the virus any more severe or reduced vaccine effectiveness compared to Delta, it said.
Eric Feigl-Ding, senior fellow at the Federation of American Scientists, told Insider that we don't know enough about AY.1 yet - "just that it's got troubling mutations."
"Let's wait and see," he said.
Dr Anurag Agarwal, director of the Delhi-based CSIR-Institute of Genomics and Integrative Biology (IGIB), one of 28 Indian labs involved in sequencing, told the BBC there wasn't any data to suggest AY.1 should cause a public-health worry panic. "We are not seeing anything worrisome yet. We are tracking it carefully, and strengthening all public health measures," he said.
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