Antibodies produced in response to some vaccines are slightly less effective against the strain of Sars-CoV-2 – the coronavirus that causes Covid-19 – found in India, according to early research.
The earliest samples of the B.1.617 variant were found in India in October and Indian authorities said in March it was spreading fast in the western state of Maharashtra.
On Wednesday, the World Health Organisation said the B.1.617 variant had been detected in 44 countries.
The UN health body classified the variant as of "global concern", citing evidence that it is more transmissible.
B.1.617.2 is considered a variant of concern in the UK because of its rapid spread there.
Studies indicate the strain found in India could spread easily and evade some antibodies from prior infection or vaccination.
This strain has eight mutations, but its most significant alterations are known as E484Q and L452R.
The former is found in the UK, South African and Brazilian variants of the coronavirus, while the latter is found in the Californian strain.
As these two strains come together in the variant found in India, it is sometimes known as a "double mutant" variant.
Researchers from the UK's University of Cambridge found the mutations confer "modestly reduced sensitivity" of about 20 per cent to antibodies produced using the Pfizer-BioNTech shot.
"This spike confers modestly reduced sensitivity to BNT162b2 [the Pfizer-BioNTech vaccine] mRNA vaccine-elicited antibodies that is similar in magnitude to the loss of sensitivity conferred by L452R or E484Q alone," they wrote in a study yet to be peer-reviewed.
While antibodies were found to be about a fifth less potent against some mutations in B.1.617, Ravindra Gupta, a virologist at the university, said this would "not render vaccination ineffective".
He was speaking in an interview with British science journal Nature.
Mr Gupta's team found some healthcare workers in Delhi who had been vaccinated by Covishield, a locally produced version of the Oxford-AstraZeneca vaccine, were reinfected.
Most cases were tied to B.1.617.
However, in laboratory tests Covishield was also found to neutralise the virus.
Researchers in Germany found people who had previously been infected with Sars-CoV-2 neutralised the strain about 50 per cent less effectively.
The blood of those who received two shots of the Pfizer vaccine was found to be about 67 per cent less potent against it.
“B.1.617 evaded antibodies induced by infection or vaccination, although with moderate efficiency.
"Collectively, our study reveals that antibody evasion of B.1.617 may contribute to the rapid spread of this variant," they wrote.
Studies into the effectiveness of Covaxin, an Indian-produced inactivated vaccine, suggest it offers protection against the strain.
There is no published research into the efficacy of the Sinopharm vaccine against it.
Experts said even if the vaccines do not prevent infection, they will limit the severity of the symptoms.
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