COVID-19 booster jabs will begin to be offered across the UK from next week.
Health Secretary Sajid Javid said he had accepted advice from the JCVI that around 30 million people should be offered a third dose – Scotland, Wales and Northern Ireland have followed suit.
The booster should be given at least six months after a second dose – with the Pfizer jab recommended.
Those eligible include over-50s, younger adults with health conditions and frontline health and care workers.
Mr Javid made the announcement in the Commons as part of an autumn and winter plan for managing COVID-19 in England.
Scotland will begin offering booster jabs for the broader group from Monday, First Minister Nicola Sturgeon said.
She said the programme “was intended to prolong the protection” of vaccines and will run alongside the flu vaccination programme.
The recommendation from the JCVI (Joint Committee on Vaccination and Immunisation) comes amid concern about waning immunity.
There are some signs protection offered by the vaccine may start dropping off several months after the second dose – with the most vulnerable groups most at risk of this.
In his statement, Mr Javid told MPs: “There is evidence that the protection offered by Covid-19 vaccines reduces over time, particularly older people who are at greater risk, so booster doses are an important way of keeping the virus under control for the long term.”
The JCVI said it was still unclear exactly how much protection does slip, but it wanted to take a precautionary approach and ensure the most vulnerable people maintain high levels of protection.
The advice is separate to the recent recommendation of third doses for people with severely weakened immune systems- something that is already being rolled out.
There is a huge amount of uncertainty about what winter will bring. In fact, it’s not even clear what the next month will bring. It was feared September could see COVID-19 cases rise, but there are no signs of that happening yet.
Big surges in infection levels are probably behind us, given the amount of immunity built up in the population.
But if current levels are sustained throughout winter, the NHS will struggle. And even a small dip in vaccine effectiveness could make a big difference to admissions – hence the booster announcement.
Then there is the concern about the return of other respiratory viruses. They were kept at bay last year by lockdowns and social distancing, but that has meant immunity to them has waned.
A virus called RSV – the leading cause of respiratory illness in young children – is already circulating at very high levels. Flu could also take off.
It is why the NHS is having to prepare for the worst, while hoping for the best.
Trials have been carried out in the UK looking at the use of booster jabs.
The JCVI said these showed Pfizer was well-tolerated and provoked a good immune response, including against new variants of the virus, such as Delta, regardless of which Covid vaccine had been given for the first two doses.
It said where Pfizer was not available a half-dose of Moderna could also be used.
For people who cannot have the Pfizer or Moderna because of issues like allergies, the AstraZeneca vaccine can be used as a booster.
A gap of six months between the second dose and the booster shot was considered the most effective for boosting protection.
The trials also showed the flu vaccine can also be given at the same time as the booster jab where that is practical – some people will be offered a flu jab before they become eligible for a Covid booster.