Two weeks after the European Medicines Agency first assured EU member states it had found no link between the Oxford/AstraZeneca vaccine and earlier reports of rare blood clots, a growing number of countries have announced new restrictions on the use of the jab.
While the UK and Austria have imposed no restrictions, France, Sweden, Finland, Canada and most recently Germany have recommended that younger people avoid the shot. In Norway and Denmark, the vaccine is still suspended.
The Irish Health Products Regulatory Authority (HPRA) said it is continuing to review “very rare reports of atypical blood disorders, which include blood clots associated with low platelets, in people vaccinated with AstraZeneca’s Covid-19 vaccine”.
No cases of blood clotting similar to those in Germany have been reported in Ireland, it confirmed.
The EMA, the World Health Organization and the UK’s Medicines and Healthcare products Regulatory Agency all state that the benefits of the vaccine outweigh any possible risks. But a rare combination of blood-related symptoms seen in a small number of people has meant some governments are proceeding with more caution.
Why are some governments still concerned?
The condition causing alarm is called sinus vein thrombosis, when blood clots in the veins that run from the brain, leading to something akin to a stroke. In the cases of concern, this has been combined with something called thrombocytopenia where a patient also presents abnormally low levels of platelets, resulting in heavy bleeding.
In Norway, health officials have reported at least six such cases among 120,000 recipients of the jab, four of whom died. In Germany, 31 cases have been reported after 2.7m vaccinations, including 29 women aged between 20 and 63, and two men aged 36 and 57. Nine of them have died.
The EMA said on Wednesday that, in total, 62 cases of these symptoms had been reported among recipients of the shot, but that this did not include the entirety of the German cases. The EMA reiterated that no causal link with the vaccine had been proven.
One hypothesis, put forward by a team of researchers in Germany, is that the AstraZeneca vaccine could be provoking an overexcited immune response in some people causing them to generate antibodies that target blood platelets.
The rare combination of blood clots and low platelet counts usually affects roughly one in 100,000 people per year in Germany, according to one of the researchers, who said that the 31 cases identified within two weeks of vaccination with the AstraZeneca vaccine point to an incidence rate 20 times higher than normal.
“It’s not just the numbers, it’s also the mechanism – it’s like a puzzle where from different angles there’s evidence that this is something unusual,” said Johannes Oldenburg, professor of transfusion medicine at the University of Bonn, who helped develop the hypothesis. Oldenburg said he believed it was “very likely that these cases originated from the AstraZeneca vaccine”.
Could age be a factor?
If the vaccine is causing this adverse reaction, the different incidence levels in different countries could be a consequence of the different age profiles of those who have received the vaccine, some experts said.
Mainland Europe, for example, has given the AstraZeneca vaccine to more people under the age of 60 than the UK, which vaccinated healthcare workers and older people first, using an even split of Pfizer and AstraZeneca shots. The UK has reported only five cases of these severe blood clots in 13.7m people injected with the AstraZeneca shot, equating to one in 3.4m people.
“It’s a complex problem of different countries using different vaccines, in different age groups and that may explain the differences,” said Saad Shakir, director of the Drug Safety Research Unit in Southampton, which is conducting a study of the AstraZeneca vaccine as it is rolled out across the UK. It was possible, Shakir said, that some younger people with more robust immune systems had experienced rare immune overreactions to the vaccine.
It is also true, experts said, that younger people, and young women in particular, were normally more susceptible to these types of rare blood clots. In the general population, the symptoms are about three times more common in women than men, and the median age of those afflicted is 33.
However, the EMA said on Wednesday that it had still not been able to identify any evidence of a link between the blood clots and specific risk factors “including age, gender or previous history”.
“At the moment, at this stage of our investigations, the link is possible and we cannot say any more than that at this point,” said EMA chief Emer Cooke. “There is no evidence that would support restricting the use of this vaccination in any population.”
The difference in the position of the EMA and some European scientists has led to varied and sometimes conflicting national advice on who should get the shot and who should not.
Have similar incidents been seen for other vaccines?
Not many. In the UK, there have been at least two reports of the same kind of blood clots in people that have received the Pfizer vaccine – 11m doses of the shot have been administered.
Oldenburg, at the University of Bonn, said he was not aware of any reports of similar incidents – or at least clusters of incidents – in people who had received any of the other Covid-19 vaccines being used in Europe, specifically the shots made by Pfizer and Moderna.
One member of the joint committee on vaccination and immunisation (JCVI) that advises the UK government said it would be “premature” to say definitively that the Pfizer shot had not led to similar problems. “Experts in Europe have looked more closely at the AstraZeneca vaccine so they’ve found more things,” the committee member said.
What is the UK doing?
Officials in the UK say there is insufficient evidence at the moment to make any changes to the vaccination policy. And even if a causal link were established, some UK-based experts said it would still make sense to continue with vaccinations as the blood clot incidents appeared to be extremely rare.
“The UK position is broadly that AstraZeneca and Pfizer are probably safe, or the risks are so small that they are massively outweighed by the benefits, so we should continue to use them,” the JCVI member said.
It was possible that in the future there could be “a case for modifying their use for younger age groups, but we’re a long way off that,” the person added, describing the European moves as “premature”.
Germany’s Oldenburg said he agreed with the UK’s decision, even though he believed strongly that the AstraZeneca shot was causing the symptoms.
“If I had a choice between immediate vaccination with AstraZeneca or waiting four weeks for Moderna, then I would choose the AstraZeneca vaccine, because the four weeks of protection far outweighs this risk,” he said.
Oxford university and AstraZeneca say their trials show that the vaccine is safe and effective and that they are continuing to monitor for side effects as the shot is rolled out. – Copyright The Financial Times Limited 2021
