Germany's vaccine commission said Thursday it could not recommend the use of AstraZeneca's coronavirus vaccine for older people, the latest twist in a row over the jab that has put Britain and the EU on a collision course.

The panel of scientific experts, called STIKO, said the vaccine should only be given to people aged 18 to 65 years old as "there is currently insufficient data to assess the efficacy of the vaccine for persons aged 65 years and older".

AstraZeneca and British Prime Minister Boris Johnson immediately defended the jabs, which have already been widely used in Britain on older people.

A spokesperson for the British-Swedish company said the latest clinical trial data for its vaccine, developed with Oxford University, "support efficacy in the over 65 years age group".

Johnson told reporters the UK's own regulator had established "that they think the Oxford/AstraZeneca vaccine is very good and efficacious, gives a high degree of protection".

AstraZeneca's vaccine has not been granted approval yet for general use in the European Union.

But the bloc's medicines regulator EMA is poised to authorise it on Friday.

The latest doubt over the vaccine came as AstraZeneca was already locked in a increasingly bitter spat with the EU over delivery problems.

Citing issues with its European factories, the company has informed the EU that it could only supply a quarter of the doses it had promised for the first quarter of 2021.

The huge delivery delay adds a further stumbling block to the EU's already sluggish rollout of the vaccine compared to Britain or the United States.

With tempers flaring, Chancellor Angela Merkel called a high-level meeting for February 1 with her cabinet, Covid-19 vaccine manufacturers and leaders of Germany's 16 states.

Countries around the world are scrambling to get hold of the life-saving jabs to inoculate their populations against the virus that has claimed more than 2.1 million lives and infected more than 100 million people.

The emergence of more contagious variants first seen in Britain, South Africa and Brazil is putting further pressure on governments to speed up their immunisation programmes.

The EU-AstraZeneca dispute escalated Tuesday when the company's chief executive Pascal Soriot said in an interview that it was prioritising supplies to Britain, which signed its contract three months before Brussels.

He argued that his company was only required to make a "best effort" to supply the bloc.

AstraZeneca and British Prime Minister Boris Johnson defended the effectiveness of its Covid-19 vaccine
AstraZeneca and British Prime Minister Boris Johnson defended the effectiveness of its Covid-19 vaccine AFP / JUSTIN TALLIS

The European Commission erupted in fury, demanding on Wednesday that AstraZeneca make up for the delays by supplying doses from its UK factories.

But Britain insists it must receive all of the vaccines it ordered -- and there are simply not enough to go round.

The EU said it would now require companies to declare any export of vaccines made in the bloc, a sign of growing distrust in AstraZeneca.

"The EU needs to take robust action to secure its supply of vaccines and demonstrate concretely that the protection of its citizens remains our absolute priority," said European Council President Charles Michel.

Germany's STIKO did not detail the data from clinical trials on the vaccine on older people.

However, prominent German media outlets Handelsblatt economic newspaper and Bild had reported that the efficacy on over-65s was below 10 percent -- claims rejected by Germany's health ministry and AstraZeneca.

A ministry spokesman said Wednesday: "A false claim does not become true just because it is repeated."

He said however that AstraZeneca trials involved fewer older people than other manufacturers.

Around eight percent of the volunteers in AstraZeneca's studies were around 56 and 69 years old and three to four percent were above 70, according to the ministry.

But "that the efficacy is only eight percent is incomprehensible and in our view, wrong," the spokesman added.

In comparison, 41 percent of participants in BioNTech-Pfizer's vaccine trials have been aged 56-85.

Britain's MHRA regulator said in its consideration of the vaccine that "there is limited information available on efficacy in participants aged 65 or over, although there is nothing to suggest lack of protection".

Mary Ramsay, head of immunisations at government agency Public Health England, also backed the AstraZeneca vaccine for older recipients.

"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.

"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."