The Pfizer coronavirus vaccine is 88% effective against the Indian variant after two doses, a study by Public Health England (PHE) has found.
Both the Pfizer and AstraZeneca jabs were found to be almost as effective against symptomatic disease from the B1617.2 strain as they are against the Kent variant after the second dose.
However, they were only 33% effective three weeks after the first dose.
UK Health Secretary Matt Hancock described the outcome as "groundbreaking", while PHE said it expects to see even higher levels of effectiveness against hospital admission and death.
The study, which took place between April 5 and May 16, found that the Pfizer vaccine was 88% effective against symptomatic disease from the Indian variant two weeks after the second dose, compared with 93% effectiveness against the Kent strain.
Meanwhile, the AstraZeneca jab was 60% effective, compared with 66% against the Kent variant over the same period.
Both vaccines were 33% effective against symptomatic disease from the Indian variant three weeks after the first dose, compared with about 50% against the Kent strain.
Some 12,675 genome-sequenced cases were included in the analysis, but only 1,054 were of the Indian variant.
The study included data for all age groups from April 5 to cover the period since the strain emerged.
Dr Mary Ramsay, head of immunisation at PHE, said: "This study provides reassurance that two doses of either vaccine offer high levels of protection against symptomatic disease from the B1617.2 variant.
"We expect the vaccines to be even more effective at preventing hospitalisation and death, so it is vital to get both doses to gain maximum protection against all existing and emerging variants."
Responding to the findings, Professor Adam Finn, professor of paediatrics at the University of Bristol said: "Overall the results are encouraging in that the vaccines are continuing to provide useful protection.
"However, protection after the first dose appears to be reduced to a potentially important degree."
