Boris Johnson has said he is not concerned by Germany ruling that the AstraZeneca vaccine should only be recommended for under 65s, as he argued the evidence shows it "provides a good immune response across all age groups".
The Prime Minister joined Public Health England (PHE) in defending the use of the jab after a draft recommendation from Germany's vaccination advisory committee on Thursday said there was insufficient data to recommend it for those aged 65 and over.
Dr Mary Ramsay, the head of immunisations at PHE, acknowledged there had been "too few cases" of coronavirus in older people in Phase 3 clinical trials to determine the level of efficacy in this age group, but said other data on immune response had been "reassuring".
Mr Johnson, during a visit to Scotland, said he does not agree with the German ruling, as he backed the advice from the UK's Medicines and Healthcare products Regulatory Agency (MHRA).
Asked if he is concerned about the verdict in Germany, the Prime Minister told reporters: "No, because I think the MHRA, our own authorities have made it very clear that they think the Oxford/AstraZeneca vaccine is very good and efficacious, gives a high degree of protection after just one dose and even more after two doses.
"And the evidence they've supplied is they think it's effective across all age groups and provides a good immune response across all age groups."
He added: "I don't agree with that."
The European Medicines Agency is expected to approve the vaccine for use in the EU on Friday, although it is not yet clear whether it will set an age limit.
But the German authorities said: "There currently is not sufficient data to assess the vaccination effectiveness from 65 years."
Dr Ramsay said the vaccines are safe and provide "high levels of protection" against Covid-19, and "particularly against severe disease".
"There were too few cases in older people in the AstraZeneca trials to observe precise levels of protection in this group, but data on immune responses were very reassuring," she added.
"The risk of severe disease and death increase exponentially with age – the priority is to vaccinate as many vulnerable people as possible with either vaccine, to protect more people and save more lives."
Oxford University, which partnered with AstraZeneca to develop the vaccine, has stressed that its jab offers high protection against severe disease and prevents people needing to go to hospital.
A Phase 3 Lancet study published in December said older age groups had been recruited later into the study so "efficacy data in these cohorts are currently limited by the small number of cases, but additional data will be available in future analyses".
In that particular analysis, only 12% of people given two doses of the vaccine in the UK arm of the trial (285 out of 2,377) were aged 56 to 69, while 9% (213) were over 70.
Some 12% of people in the control group (given a dummy vaccine) were also aged 56 to 69 while 9% were over 70.
Older people made up similar proportions in the Brazilian section of the trial, which was made up of 4,088 people.
Previous work published in November included findings for 560 people.
Of these, 160 were aged 18 to 55, 160 were aged 56 to 69, and 240 were 70 or older.
Those results found that all age groups, including older people, had an immune response to the vaccine after two doses.
Earlier this week, a report in German business daily newspaper Handelsblatt said AstraZeneca's vaccine was thought to be only 8% effective among the over-65s.
AstraZeneca and the vaccines minister Nadhim Zahawi dismissed the report as "incorrect" and "untrue".
Meanwhile, Downing Street said the UK's chief scientific adviser, Sir Patrick Vallance, had told the Cabinet that the Oxford/AstraZeneca vaccine had been shown to be effective in younger and older people.
A No 10 spokesman said: "The chief scientific adviser set out that the Oxford/AstraZeneca vaccine remains both safe and effective and that the trials showed similar immune responses in both younger and older adults."