India has classified Delta coronavirus variant carrying a mutation as a "variant of concern". It has an extra genetic tweak that could allow the virus to evade the human immune system.
India has found around 40 cases of the Delta coronavirus variant carrying a mutation that appears to make it more transmissible, and advised states to increase testing.
The Delta Plus variant, also known as AY.1, spreads more easily and seems to be affecting lungs, India's Health Ministry warned on Wednesday.
Indian authorities have classified the new mutation as a "variant of concern", which means it meets at least one of the several criteria such as increased transmission or resistance of vaccine to make it worrisome.
Is it more lethal?
We don't know for sure.
"Based on the recent findings of INSACOG (Indian SARS-CoV-2 Genomic Consortia), the Health Ministry has alerted and advised Maharashtra, Kerala and Madhya Pradesh regarding the Delta Plus variant found in these states," the ministry said in a statement.
Delta Plus was first reported in a Public Health England bulletin on June 11. It was initially identified in Europe in March but its discovery has just recently come to light.
It's related to the Delta variant that surfaced in India and has acquired the spike protein mutation called K417N, which is also found in the Beta variant, first identified in South Africa.
The Delta variant, first identified last year, was responsible for the deadly second wave that overwhelmed India's health infrastructure.
Now there are fears that this new mutation can lead to a third wave of infections.
Some scientists worry that the mutation, coupled with other existing features of the Delta variant, could make it more transmissible.
"The mutation K417N has been of interest as it is present in the Beta variant (B.1.351 lineage), which was reported to have immune evasion property," India's Health Ministry said.
Shahid Jameel, a top Indian virologist, said the K417N was known to reduce the effectiveness of a cocktail of therapeutic monoclonal antibodies.
What are the experts saying?
As of June 16, at least 197 cases have been reported from 11 countries including Britain, Canada, India, Japan, Nepal, Poland, Portugal, Russia, Switzerland, Turkey, and the United States, according to Reuters news agency.
Studies are ongoing in India and globally to test the effectiveness of vaccines against this mutation.
"WHO is tracking this variant as part of the Delta variant, as we are doing for other Variants of Concern with additional mutations," the World Health Organization (WHO) said in a statement sent to Reuters.
"For the moment, this variant does not seem to be common, currently accounting for only a small fraction of the Delta sequences ... Delta and other circulating Variants of Concern remain a higher public health risk as they have demonstrated increases in transmission," it said.
Some experts say that New Delhi has rushed ahead in declaring the Delta Plus as a "variant of concern" as there was not enough data to back it up.
"There is no data yet to support the variant of concern claim," Dr Gagandeep Kang, a virologist, told BBC.
But India has warned that regions where it has been found "may need to enhance their public health response by focusing on surveillance, enhanced testing, quick contact-tracing and priority vaccination."
There are worries Delta Plus would inflict another wave of infections on India after it emerged from the world's worst surge in cases only recently.
"The mutation itself may not lead to a third wave in India — that also depends on Covid-appropriate behaviour, but it could be one of the reasons," said Tarun Bhatnagar, a scientist with the state-run Indian Council for Medical Research.