People in their 30s will be offered an alternative to the Oxford/AstraZeneca vaccine, UK government officials confirmed on Friday, as declining Covid-19 infection rates mean the risk of a rare blood clotting condition linked to the jab may outweigh the dangers of the disease.

The Joint Committee on Vaccination and Immunisation (JCVI) announced it had recommended to the government that, when available, the BioNTech/Pfizer or the Moderna vaccines should instead be offered to healthy people under the age of 40.

“People in their 30s should be preferentially offered an alternative vaccine where that is possible and where it does not result in a delay to the vaccination campaign,” said Professor Wei Shen Lim, chair of the JCVI.

He added that the “strength of the vaccine programme over the past few weeks”, and the increasing evidence that the jabs prevent transmission as well as infection, had changed perceptions about the dangers of the virus to the young and a third wave of the pandemic.

Lim said, however, that should vaccine supply become more constrained or if a third wave is more severe than anticipated, “any vaccine is preferable to a vaccine offered late”.

Britain abruptly changed tack last month on the AstraZeneca jab, the mainstay of its inoculation programme, after the JCVI advised that, all healthy individuals under the age of 30 should be offered an alternative vaccine, if available.

Denmark has dropped its use altogether while a number of other European countries have limited it to older people as evidence has mounted over the past few weeks that a rare blood clotting condition more common in the young could be linked to the AstraZeneca vaccine.

The change in guidance for the under-40s in the UK will deal a further blow to Oxford university and the Anglo-Swedish pharmaceutical company, which set out to produce a low-cost vaccine for the world but have faced multiple setbacks.

Professor Jonathan Van-Tam, deputy chief medical officer for England, said the change in guidance was not expected to affect the speed of the UK’s vaccination campaign. “We are still on target to offer a first dose to all adults by the end of July,” he said.

Analysis by the Medicines and Healthcare products Regulatory Agency (MHRA) found that while the incidence of a rare and sometimes fatal blood clotting condition is roughly one in 100,000 recipients of the AstraZeneca vaccine for the population as a whole, this rises to roughly one in 60,000 for people in their 30s.

Similarly, while the condition resulted in deaths in about 2 per million people who received the AstraZeneca vaccine in the wider population, deaths in people aged between 30 and 39 were 4.5 in a million.

The MHRA stressed that the balance of risk and reward was much more favourable for those in their 40s, for whom the incidence rate of these clots is roughly 1 per 100,000 people.

The JCVI has also concluded that there are no safety concerns relating to the second dose of the AstraZeneca vaccine — if someone has already been given their first dose, they should also be given their second.

UK government data released on Thursday showed that a total of 242 cases of the rare blood clotting events had been identified up to April 28 among Britons who have had at least a first dose of the AstraZeneca vaccine, 33 more than the week before. These 242 cases included 49 deaths.

Two-thirds of the people affected by the condition were under the age of 60.

By contrast, Public Health England analysis indicates that the vaccination campaign has prevented more than 10,000 deaths in England up to the end of March.

“Our position remains that the benefits of the Covid-19 vaccine AstraZeneca, with its associated risk of hospitalisation and death, continue to outweigh the risks for the vast majority of people,” said Dr June Raine, chief executive of the MHRA.

Raine added that there is now increasing evidence that the rare blood clotting condition does afflict women more commonly than men, and added that the MHRA was looking at the data on this “very carefully”.

The latest data from the Office for National Statistics, released on Friday, showed that coronavirus infections have continued to drop across the UK. In England, roughly one in 1,180 people were estimated to have Covid-19 in the week ending May 2, down from one in 1,010 the week before.

Oxford university said it was for relevant national bodies to decide how to best vaccinate their populations. AstraZeneca did not respond to a request for comment.