All over-40s in the UK will be offered a third dose of a Covid vaccine, after advice from the government scientists.
The move would top up protection and help limit the spread of the virus over winter.
Three doses cuts the risk of infection by more than 93%, according to new data from the UK Health Security Agency.
The Joint Committee on Vaccination and Immunisation also said 16- and 17-year-olds, initially offered only a single dose, should now receive a second.
So far, 12.6 million people have had a booster dose.
They have been given to the over-50s, front-line medical staff and people with health conditions that put them at greater risk.
Prime Minister Boris Johnson said it would be an “utter tragedy” if double vaccinated people became seriously ill or died “because they allowed their immunity to wane”.
He said there was “nothing in the data” to suggest a lockdown or Plan B was needed at the moment; despite “storm clouds” gathering in Europe, where cases are climbing.
