Ministers have piled pressure on the vaccines watchdog to approve a large-scale programme of Covid booster injections in time for winter, as the number of people in hospital with the virus exceeded 8,000 for the first time since March.

On Thursday the UK’s medicines regulator granted emergency approval for the Pfizer and AstraZeneca vaccines to be used as third shots to tackle potentially waning immunity, also putting pressure on the Joint Committee on Vaccination and Immunisation (JCVI) to approve a new jab programme.

Hours later, the health secretary, Sajid Javid, said he was confident that such injections would begin imminently. “We are heading towards our booster programme,” he said. “I’m confident that our booster programme will start later this month, but I’m still awaiting the final advice.”

The JCVI is expected to announce imminently whether it has approved boosters, and if so on what scale. Members of the committee, which advises UK health departments, met virtually for more than four hours on Thursday and were briefed on interim results from the Cov-Boost study.

While the study’s results have not yet been made public, they were cited as supporting evidence by the Medicines and Healthcare products Regulatory Agency (MHRA) in its emergency approval of the vaccines to be used as boosters.

Javid and ministerial colleagues are believed to be impatient to begin a mass rollout of booster jabs, as has already happened in Israel. However, the JCVI could disagree; it has described the issues under discussion as complex and containing numerous ethical implications.

The JCVI has already approved third jabs for around 500,000 very clinically vulnerable adults and older children. Even if it does approve boosters, it could decide that these should initially be limited to older adults, or those with other health conditions.

Last week the JCVI declined to approve the use of Covid vaccinations for all 12- to 15-year-olds, something also strongly sought by ministers, instead expanding the use of jabs for those in the age group with severe health conditions.

The decision to withhold mass vaccinations for older children could still be reversed by a review of wider evidence by the chief medical officers of the four UK nations, which is also due to report imminently.

The MHRA’s announcement stressed that while it had approved booster vaccines in principle, it remained the JCVI’s decision over how, if at all, they could be used. “This is an important regulatory change as it gives further options for the vaccination programme, which has saved thousands of lives so far,” said Dr June Raine, the MHRA’s chief executive.

“It will now be for the JCVI to advise on whether booster jabs will be given and, if so, which vaccines should be used.”

While some scientists welcomed the MHRA’s move, others questioned whether it was ethical to provide millions of extra jabs to people with existing immunity when so many people worldwide had not yet received any vaccinations – a consideration that is not in the JCVI’s remit.

“By any standards this is good news,” said Danny Altmann, a professor of immunology at Imperial College London. “As we see in daily breakthrough caseload, Delta has really stress-tested our defences. While UK cases are held down to about 40,000 a day as we head into autumn, there’s clearly little room for complacency. Data from Israel has already shown clearly that a third dose can enhance protection substantially to bring breakthroughs right down.”

But Prof Andrew Hayward, the director of the UCL institute of epidemiology and healthcare, suggested that while the announcement was good news for countries with a plentiful supply of jabs, it could have downsides when it comes to fair distribution of vaccines around the world.

“Those who have had any doses of vaccine will be at much lower risk of severe Covid-19 than those who have had none – so whilst the booster dose is likely to further increase protection in those receiving it, the dose would save more lives if given to someone in a country who has not yet had the opportunity to get any doses,” he said.

“This is one reason not to consider a general, whole-population approach to booster doses, but to focus on those who are most vulnerable – [such as] the elderly and those who are extremely clinically vulnerable – who were also vaccinated earlier and have therefore had longer for antibodies to wane.”