Countries that suspended the rollout of the Oxford-AstraZeneca vaccine will re-start immunisation programmes after they analyse data on the jab, experts have predicted.
A number of countries, mostly in Europe, have stopped using the British-developed shot amid concerns that it could cause blood clots in those receiving it.
However, Dr Andrew Freedman, an infectious diseases specialist at Cardiff University, said that when such large numbers people are being studied, it would be normal to find blood clots across the population.
“It’s unlikely to be a causal relationship,” he said.
“I expect they will resume the use of the AstraZeneca vaccine once they’ve had a chance to look at the cases.”
The medicines regulator in Norway has reported four serious cases of blood clotting in adults who received the jab, while there have been reports of deaths from blood clots in Austria, Denmark and Italy.
More than 10 European countries, as well as Indonesia, have suspended the use of the vaccine while they investigate data from health authorities about blood clots. Thailand last week said it would delay its rollout, but has since said this will go ahead.
However, the World Health Organisation has insisted the jab is safe and AstraZeneca too has said there is no evidence of an increased risk of blood clots.
The company said that among 17 million doses administered in Europe, there have been 37 cases of pulmonary embolism [a clot in a blood vessel in the lungs] or deep-vein thrombosis, fewer than normally expected among a group that size.
The European Medicines Agency and the UK’s regulator, the Medicines and Healthcare Products Regulatory Agency, also say there is no evidence the blood clots were caused by the vaccine.
Speaking to the BBC on Monday, Prof Andrew Pollard, head of the Oxford Vaccine Group which developed the jab, maintained the shot did not increase the risk of blood clots and said the desire to pause rollouts should be balanced “against the huge risks of Covid”.
“We’ve got very reassuring evidence there’s no increase in blood clots here in the UK, where most doses in Europe have been given,” he said, referencing the more than 11m doses of the jab given in the UK, the largest of any country.
Although approved for use in people of all ages by the EMA, the Oxford-AstraZeneca jab has had a lukewarm reception in Europe, partly because clinical trials included relatively few older people.
In late January the French president, Emmanuel Macron, described it as “quasi-ineffective” in over-65s and several European countries decided not to administer it to older residents.
These age restrictions have typically been lifted as more data has come in, but there have been reports of some residents turning the vaccine down.
Switzerland, which is not part of the EU, has yet to give the green light for the vaccine to be given to people of any age.
Dubai Health Authority approved the jab for anyone aged 18 to 65 in early February and about a month later removed the upper age limit.
Prof David Taylor, professor emeritus of pharmaceutical and public health policy at University College London, said countries that had suspended use of the vaccine were “being over the top”.
“It’s going to be likely that people who have had the vaccine have blood clots [by chance],” he added. “I think they’re being rather silly”.
Covid-19 itself is thought to increase the risk of blood clots, and patients are sometimes prescribed anticoagulant medication as a result.
In February, the Oxford-AstraZeneca jab became the second vaccine against the coronavirus to be given approval for emergency use by the World Health Organisation, although countries had starting using it weeks earlier after their own regulators gave the green light.
Because it is relatively cheap to manufacture and can be kept in refrigerators – unlike some other shots that require extreme cold temperature storage – it is particularly suited to rollouts in developing nations.
Given in two doses, it is made from a type of virus called an adenovirus that normally infects chimpanzees but that is unable to replicate or cause disease.
The adenovirus has had genetic material added so that it causes human cells to produce coronavirus spike proteins, the immune response to which provides protection against Covid-19.