The recommendation, which needs ministerial approval, also suggests second doses for 12 to 15-year-olds.
Covid booster jabs should be offered to all over-18s to help stop a potential wave driven by the new variant Omicron, UK government advisers say.
The Joint Committee on Vaccination and Immunisation said the minimum gap between the second dose and booster should also be reduced to three months.
The experts said boosters should be prioritised in order of vulnerability.
And they recommended children aged 12 to 15 should be invited for a second jab three months after their first.
The JCVI also recommended severely immunosuppressed people should be offered a fourth does of the vaccine as a booster. They are currently receiving three jabs.
Prof Wei Shen Lim, chair of the JCVI, said at a Downing Street briefing that he was not predicting the new variant would take hold in the UK but they wanted to be in the best possible position if there was an increase in infection.
He said: “With any vaccine during a pandemic, we get the greatest benefit for individuals and society if the vaccine is deployed before the wave starts. We want to provide boosters early enough… before any possible wave.”
The advice has been given to ministers in all parts of the UK. The JCVI only gives recommendations and the final decision on measures to combat Covid lies with the politicians.
Early evidence suggests the new Omicron variant – initially reported to the World Health Organization from South Africa on Wednesday – has a higher re-infection risk.
Eleven cases of the Omicron variant have now been detected in the UK. The UK Health Security Agency said the latest two found have links to travel in southern Africa. They were detected in the Camden and Wandsworth areas of London.
Prime Minister Boris Johnson indicated the government would accept the JCVI’s recommendations on Saturday when he unveiled new rules on face masks and isolation rules to contain the spread of the new variant.
The rules are due to come in to force in England on Tuesday.