An additional booster dose will be offered to all adults over-75 and the most vulnerable over-12s in the UK this spring.
The UK’s vaccines advisers said an extra dose would help top up their protection against severe Covid-19.
Many of the oldest received their latest shot back in the autumn and immunity may now be waning, it said.
An autumn booster programme, aimed at a wider group of people, is also planned later this year.
Up until now, only people with severely weakened immune systems had been eligible for a fourth dose – three doses plus a booster.
Those now being offered a second booster this spring, to be administered six months after their previous dose, are:
Adults will be offered a Pfizer or Moderna vaccine, while children aged 12-18 will receive Pfizer.
Around 7.2 million people in the UK aged over 75, who have already had their primary course of Covid vaccines, will be eligible for the extra spring booster.
Another half a million people who are immunosuppressed, with diseases such as blood cancer or who’ve had an organ transplant or are receiving chemotherapy, will also be eligible for the additional booster.
The JCVI said vaccinating these groups was a “precautionary” move and did not mean there was any current danger to their health.
But because people in these groups are at higher risk from Covid-19, have weaker immune systems than other people and were last vaccinated in September of October 2021, their protection from vaccines might be waning more quickly.
Data suggests that older people who have had two doses of a Covid vaccine have about 45% protection against hospital admission with Omicron, rising to 90% straight after their first booster.
Ten weeks later, that protection has dropped to about 88% but the JCVI believes that even a small drop-off in protection among vulnerable and older people can have a large impact, including on hospital admissions and the NHS.
Winter is seen to be the season which poses the greatest threat from Covid, particularly for older adults, the NHS and case homes.
Prof Wei Shen Lim, chair of Covid vaccination at the JCVI, said: “Last year’s booster vaccination programme has so far provided excellent protection against severe Covid-19.
“To maintain high levels of protection for the most vulnerable individuals in the population, an extra spring dose of vaccine is advised ahead of an expected autumn booster programme later this year.”
Health and Social Care Secretary Sajid Javid said he had accepted the JCVI’s advice and asked the NHS to prepare to offer a vaccine to those eligible. He added that further details would be sent out in due course.
“We know immunity to Covid-19 begins to wane over time. That’s why we’re offering a spring booster to those people at higher risk of serious Covid-19 to make sure they maintain a high level of protection,” he said.
“It’s important that everyone gets their top-up jabs as soon as they’re eligible.”
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