People who have been infected with Covid-19 are more likely to be reinfected by the Delta variant, research finds.
The French study, published in the journal Nature, found the variant was four times more likely to overcome the protection afforded by antibodies from previous infection than the Alpha variant, first detected in England.
British health authorities have already said the Delta strain could be up to 60 per cent more infectious than Alpha.
The study, carried out by the Institut Pasteur in Paris, found a single dose of either the Pfizer-BioNTech or AstraZeneca-Oxford University vaccines was “poorly or not at all efficient” against Delta and Beta (first detected in South Africa).
One dose provided on average just 10 per cent protection in a sample group of 103 people.
However, protection increased significantly after two doses.
The study found the vaccines generated a neutralising response of 95 per cent, although the antibodies were three to five times less potent against Delta compared with Alpha.
France on Friday said the Delta variant would probably account for most new cases in the country from this weekend.
French Health Minister Olivier Veran said the variant represented nearly 50 per cent of all Covid-19 cases.
In England, the variant accounts for 99 per cent of all cases that have been genetically sequenced, with Public Health England data showing cases of the variant have increased by 54,268 in the past week.
More than 86 per cent of adults in the UK have received a first shot of a Covid-19 vaccine, while nearly 65 per cent are fully vaccinated with two doses, according to the latest government figures.