Commuters exit underground transport in cental London Photograph:( AFP )
UK Health Security Agency (UKHSA) said AstraZeneca and Pfizer-BioNTech provided much "lower levels of protection against symptomatic infection" compared to Delta.
As Omicron cases in the UK continue to surge, UK's health body has warned Omicron cases may account for 50 per cent of all COVID-19 infections in the UK by mid-December.
"If Omicron continues to grow at the present rate, Omicron case numbers are projected to reach parity with Delta cases in mid-December," the UK health security agency said.
UK Health Security Agency (UKHSA) said AstraZeneca and Pfizer-BioNTech provided much "lower levels of protection against symptomatic infection" compared to Delta. However, the report said "effectiveness against the new variant" appears to increase after a booster dose while emphasising that those over 40 should take the booster dose.
The UK health security agency said Omicron was detected in wastewater in the UK between November 26 and November 28. The report said the Omicron variant has a "transmission advantage" compared to Delta.
Watch: WHO warns not to underestimate Omicron
The agency said Omicron cases continues to grow rapidly in all regions of England. A finding earlier had revealed 30 per cent of all COVID-19 cases in London were due to Omicron.
UK health secretary Sajid Javed told parliament on Tuesday that according to the UKHSA the number of daily infections due to Omicron was "42 times higher at 200,000" even though only 4,713 confirmed were reported.
Javed conceded that "the travel red list is now less effective in slowing the incursion of Omicron from abroad" as the travel ban was lifted for African countries. British Prime Minister Boris Johnson announced "Plan B" measures to tackle the new variant as the country continues to battle the virus.
(With inputs from Agencies)