Updated advice from the Joint Committee on Vaccination and Immunisation (JCVI) says eligibility for booster doses of COVID-19 vaccine should expand immediately to all adults aged 18 to 39 years old.
The updated advice says booster vaccination - with either the Pfizer or Moderna vaccines - should continue to be rolled out 'in order of descending age groups' and prioritising those in at-risk groups, but shortens the timescale within which booster doses can be offered.
Plans to expand the booster campaign come as GP leaders appeal to ministers to reduce administrative pressure on general practice to allow a greater focus on the vaccination campaign.
COVID-19 booster vaccination
Booster doses should not be given 'within three months of completion of the primary course' of COVID-19 vaccination, the advice says - halving the previous recommendation that boosters should take place six months after primary vaccination.
Patients with severe immunosuppression who have received three doses as part of their primary course can also be offered a booster jab three months after their third dose.
The JCVI has also recommended that all children and young people aged 12 to 15 years old should be offered a second dose of the Pfizer COVID-19 vaccine 'at a minimum of 12 weeks from the first dose'.
It said that a reduction in the interval to eight weeks could be approved 'if the emerging epidemiological data supports this' - and that this shorter timeframe could also be applied for 16- to 17-year-olds.
A statement from the committee said: 'The overall intention of the measures advised above is to accelerate the deployment of COVID-19 vaccines before the peak of any impending Omicron wave.
'There is currently no data to indicate that Omicron infection is associated with a change in the pattern of susceptibility to serious COVID-19 (hospitalisation and death). Persons of older age, or who are in COVID-19 at-risk groups are likely to remain at higher risk from serious COVID-19; therefore, vaccination should be prioritised accordingly.
'Continued efforts should be made to offer COVID-19 vaccination (first, second and booster doses) to adults who have yet to receive any COVID-19 vaccinations.'
Deputy CMO Professor Jonathan Van Tam told a Downing Street press conference: 'We don't know what is going to happen next. The next three weeks will be weeks of scientific uncertainty.
'While we wait for the mist to clear on what this concerning variant means, there is no time to delay. Vaccine boosting is the thing we can do most easily while we wait for the science mist to clear.'