Experts warned of damage to confidence in the UK’s vaccine programme after 10 million adults under 30 were told they will be offered an alternative to the Oxford/AstraZeneca jab following concerns over rare blood clots.

Healthy 18 to 29-year-olds who are not at high risk of Covid should have the option of a different jab if one is available in their area, the government’s joint committee on vaccines and immunization (JCVI) said weeks after some European countries suspended the use of AstraZeneca jabs in younger people.

For older people, the benefits of the vaccine – the most widely-used in the UK – far outweigh the risks, the JCVI added. The UK has recorded 79 rare blood clots cases, 19 of whom died, out of 20m AstraZeneca jabs administered.

England’s deputy chief medical officer, Prof Jonathan Van-Tam, called the move “a course correction” and said there should be little or no impact on the vaccine rollout timeline, though he warned that under-30s could face short delays in getting inoculated.

Boris Johnson tweeted: “We will follow today’s updated advice, which should allow people of all ages to continue to have full confidence in vaccines, helping us save lives and cautiously return towards normality.”

We will follow today’s updated advice, which should allow people of all ages to continue to have full confidence in vaccines, helping us save lives and cautiously return towards normality. 3/3

— Boris Johnson (@BorisJohnson) April 7, 2021

The recommendation came as it was confirmed that the European regulator is examining whether other vaccines using similar technology to the AstraZeneca jab pose any risk.

There had been three cases of venous thromboembolism blood clots with low platelets involving the Johnson & Johnson jab, a European Medicines Agency (EMA) official said.

Symptoms of the rare brain blood clots include severe headaches and blurred vision, and most cases occur within two weeks of a jab – but such events are treatable if medical help is sought, experts said.

In the UK up to 31 March, there were 79 reports of these rare blood clots with low platelets – some but not all of them in the brain, it was revealed on Wednesday. Of those affected, 19 people died, although it is not known if the blood clots were the cause in every case.

More were women – 51 – and they were all aged 18-79. Three were under 30. But the recommendation of an alternative vaccine for that age group is because their risk from Covid itself is very low.

In older age groups, the experts believe, the benefits of vaccination significantly outweigh the rare side-effect risk, but in younger people “it is more finely balanced”.

Dr June Raine, CEO of the Medicines and Healthcare products Regulatory Authority (MHRA), said the risk was “extremely small” and the authority had not yet concluded that the vaccine was responsible.

“The evidence is firming up. While it is a strong possibility, more work is needed to establish beyond all doubt that the vaccine has caused this side-effect,” she said.

There are concerns, however, that confidence in the AstraZeneca jab has been hit.

“Today’s decision is a severe blow to the public’s vaccine confidence, which is already fragile,” said Dr Chris Papadopoulos, principal lecturer in public health at the University of Bedfordshire. It might be the right decision, but needed to be coupled to efforts to counter vaccine hesitancy, he added.

Prof Martin Hibberd, of the London School of Hygiene & Tropical Medicine, said it was a sensible decision. “However, I would like to see the evidence that the other vaccines are safer.”

The Royal College of Midwives said young people and pregnant women would be concerned.

“Although pregnant women who are clinically extremely vulnerable are eligible for the vaccine, those under 30 have seen their options severely limited, as the Pfizer/BioNTech vaccine is not approved for use for them,” said its executive director, Birte Harlev-Lam.

Pregnant women should discuss vaccination with their doctor. Those who have any history of blood clots should not have the AstraZeneca jab.

It came as the EMA said the rare blood clots would be listed formally as a side-effect of the AstraZeneca vaccine, though it did not announce any restrictions on use. Several EU countries, including France and Germany, have already limited use to citizens aged over 55 or 60, or suspended its use entirely.

Emer Cooke, executive director of the EMA, said: “In the UK, I cannot comment on the decision-making to restrict to a certain age but what I can tell you is there is a lot more use in the younger age groups in the UK than in the EU at the moment and we will certainly take this into account in our further evaluations.”

Asked why European countries have different stances from the UK, Adam Finn from the JCVI said Britain had “extremely detailed data” based on a high number of administered AstraZeneca jabs.

“I think other countries in Europe that have seen clusters of cases … they are not in such a good evidence-driven position to make their judgments,” he said, adding that “the risk-benefit [equation] does vary … from one country to another”.

The EMA said it could not identify the cause of the blood-clotting event, which was mostly, but not entirely, in women under 60.

It is advising that healthcare professionals and people getting the vaccine should be made aware of the issue and the symptoms of the clots, which range from shortness of breath and chest pain to persistent headaches and blurred vision.

“It is of great importance that healthcare professionals and people coming for vaccination are aware of these risks and look out for signs or symptoms,” said Cooke.

Like the EMA, the MHRA is a regulator and an adviser on safety and efficacy to governments.

The UK recommendation that under-30s should be offered an alternative vaccine comes from the JCVI. Its head, Prof Wei Shen Lim, said it had only made the recommendation to government “out of the utmost caution rather than because we have any serious safety concerns”.

Dr Peter Arlett, the head of the EMA data analytics and methods taskforce, said the agency was examining whether other vaccines posed any risk, citing cases of rare blood clots involving the Johnson & Johnson jab.

“There have been three cases with the Johnson & Johnson vaccine of blood clots associated with low platelets which have some similarities to these cases that we’ve been describing today,” he said.

“However, the numbers are extremely small compared with the 5 million patients that have received the Johnson & Johnson vaccine worldwide. This is, however, under close scrutiny, the [committee] is looking at it carefully, and I think it would be fair to say there’s intensive monitoring of this issue across the vaccines.”

A UK government spokesperson said: “The Oxford/AstraZeneca vaccine is safe, effective and has already saved thousands of lives.

“Everybody who has already had a first dose of the AstraZeneca vaccine should receive a second dose of the same brand, irrespective of age, except for the very small number of people who experienced blood clots with low platelet counts from their first vaccination.”