France, Germany and Italy are the latest countries to announce a temporary pause on the use of the Oxford/AstraZeneca coronavirus vaccine while reports of blood clots are investigated.

Both the EU regulator – the European Medicines Agency (EMA) – and the World Health Organisation (WHO) say there is no evidence the vaccine causes blood clots and countries should carry on using it.

Britain, Australia, Thailand and others say they have no plans to stop rolling out the AstraZeneca jab, which was developed by scientists at Oxford University.

But the list of states that have decided to pause the use of the AZD1222 vaccine is growing longer. What is going on?

Reports of blood clots

Some people who have been vaccinated will always fall ill or even die afterwards, simply by chance. It’s usually hard to prove that the vaccine caused the illness.

Regulators investigate reports of serious incidents to see if more have occurred in vaccinated people than would be expected in the general population. There is no general rule that vaccinations have to be halted while these investigations take place.

Last week the Norwegian Medicines Agency said that it was investigating an unexpected fatal brain haemorrhage in a patient who had received the AstraZeneca jab as well as “several” reports of symptoms that could be a sign of reduced blood platelet counts.

Over the weekend the agency said it had received “three more reports of severe cases of blood clots or brain haemorrhages in younger people who have received the AstraZeneca vaccine”.

Denmark was the first country to announce it was temporarily suspending its use of the vaccine and now other countries including France, Germany, Italy and the Republic of Ireland have followed suit.

New evidence?

The Norwegian authorities said “similar incidents” had been reported in other European states.

The EMA said there had been 30 reports of “thromboembolic events” among nearly 5 million people given the AstraZeneca vaccine in the European Economic Area. It’s not clear how serious these cases were.

Several countries who announced suspensions made it clear that they were responding to the reports from Norway rather than reacting to fresh cases among their own populations.

The Dutch authorities said no new cases had been found in the Netherlands, and Ireland’s deputy chief medical officer Dr Ronan Glynn said there had been no reports of blood clot events in Ireland.

Some countries have said their suspensions will be brief. Dr Glynn said: “It may be nothing, we may be over-reacting and I sincerely hope that in a week’s time we are accused of being overcautious.”

French President Emmanuel Macron said France’s decision to halt the use of AZD1222 came ahead of a statement from the EMA expected on Tuesday.

Higher risk for vaccinated people?

Every week the UK government publishes so-called “yellow card” reports of adverse events among people given the AstraZeneca and Pfizer vaccines here.

The British authorities say the safety results so far for both vaccines has been “as expected from the clinical trials”. Reports of ill health always have to be seen within the context of the large numbers of people who have been vaccinated.

AstraZeneca said on Sunday that out of 17 million people who have received its vaccine across the UK and the EU, there have been 15 cases of deep vein thrombosis and 22 events of pulmonary thrombosis (both serious blood clotting disorders).

The drug company said these numbers were “much lower than would be expected to occur naturally in a general population of this size”.

The Cambridge statistician Professor Sir David Spiegelhalter agreed today, saying: “Deep vein thrombosis happens to one in 1,000 people per year of all ages.

“So, out of those 17 million jabs, we would expect at least 17,000 of those people to get a deep vein thrombosis some time in the year.

“So that means that there will have been – and you can pretty well guarantee it – 350 people who have had an AstraZeneca jab then had a deep vein thrombosis in the week following that.

“I think what’s surprising is that only 15 have been reported as a possible adverse effect.”

Bad batch?

A number of EU countries who announced temporary pauses last week specified that they were only concerned about one batch of the vaccine.

But AstraZeneca said a review of all the safety data available showed “no evidence of an increased risk of pulmonary embolism, deep vein thrombosis or thrombocytopenia, in any defined age group, gender, batch or in any particular country”.

AstraZeneca riskier than Pfizer?

AstraZeneca said its safety results for blood clotting conditions were “similar across other licensed COVID-19 vaccines”.

Professor Stephen Evans from the London School of Hygiene and Tropical Medicine said the latest publicly available data showed there were 35 reported cases of thrombocytopenia (a low blood platelet disorder) out of 54,000 “yellow card” reports after nearly 10 million AstraZeneca vaccinations.

For the Pfizer vaccine there were 22 cases out of 33,000 reports and almost 11 million doses administered.

Prof Evans said: “It is clear that the proportion of reports for this bleeding disorder is not different in the two vaccines.”

More harm than good?

Professor Evans added that the Norwegian authorities had not made it clear that blood disorders are common in patients who are suffering from Covid-19.

“Unless we are sure that those who suffered these unfortunate events very definitely did not have COVID-19 then it would seem to be premature to suggest it was the vaccine that caused these events.”

This means it’s possible that suspending a vaccine which prevents severe Covid could actually increase the risk of blood disorders at a time when many European countries are seeing an upsurge in coronavirus cases.

Ethical dilemma

It’s notable that international organisations including the EMA, the WHO, and the International Society on Thrombosis and Haemostasis have all called for the continued use of the AstraZeneca vaccine.

But many national governments have ignored the advice to carry on vaccinating, and have decided to pause while the possible risk is investigated.

Dominic Wilkinson, Professor of Medical Ethics at Oxford University, said it was possible to justify both courses of action on ethical grounds, but he feared that politicians making the decisions were “twitchy” about public fears over vaccine safety.

He told FactCheck: “Politicians who are twitchy will not always make rational decisions.

“Sometimes people worry about the harms that might be caused by the vaccine, but they don’t worry enough about the harms that could be caused by withholding the vaccine. From a philosophical perspective, these harms are equally weighty.

“I think it’s striking that the World Health Organisation has been very strong with their message about this and has reached a very different conclusion from governments.

“I think the WHO is perhaps politically less sensitive to anxiety in the population about vaccine harms and politicians are very sensitive to this anxiety.”

Professor Adam Finn from Bristol University, a member of the Joint Committee on Vaccination and Immunisation, told FactCheck: “I think it boils down to individuals and groups being asked to make calls they are just not used to making in very unusual circumstances – in those circumstances, caution (and sometimes over-caution) can often prevail.

“It’s possible that individual circumstances of different countries may also be playing a part – for example if you aren’t using the vaccine to any great extent, there isn’t so much to be lost by temporarily stopping its use.

“However, the regulatory bodies – MHRA and EMA and WHO – are all speaking with one voice – that there’s no safety signal and no need to suspend programmes deploying this vaccine.

“To me at least, it’s surprising that individual countries seem to be ignoring that advice and instead looking sideways at each other.”